Evolutionary Biology Human Evolution
by
Bernard Wood
  • LAST REVIEWED: 19 May 2017
  • LAST MODIFIED: 30 October 2019
  • DOI: 10.1093/obo/9780199941728-0050

Introduction

The study of human evolution involves (1) understanding the evolutionary context and the circumstances surrounding the origin of the branch of the Tree of Life (technically referred to as a clade) whose only extant taxon is modern humans, (2) recognizing the extinct species that are more closely related to modern humans than to the closest living apes (i.e., chimpanzees and bonobos), (3) reconstructing the morphology and behavior of those species, (4) determining how they are related to each other and to modern humans, (5) investigating the factors and influences that shaped their evolution, and (6) reconstructing the origin(s) of modern human anatomy and behavior. The study of the fossil evidence for human evolution is traditionally referred to as hominid paleontology, which reflected the then-prevailing conventional wisdom that the differences between modern humans and the great apes were profound enough to merit being recognized at the level of the family, with modern humans in the family Hominidae, and the great apes in the family Pongidae. But the molecular evidence is consistent with a particularly close relationship between Homo sapiens (the formal Linnaean name for modern humans) and two of the great apes, chimpanzees and bonobos. In the light of this compelling evidence, many researchers use the tribe (the taxonomic category below the level of the family and above the level of the genus) Hominini to accommodate the species and genera more closely related to modern humans than to chimpanzees and bonobos. So, in the new terminology the study of the human fossil record should be referred to as hominin paleontology. The study of the artifacts (e.g., stone and bone tools, drawn and carved images, early structures, evidence of decoration, etc.) made in prehistoric times is called prehistoric archaeology. In the United States the combined study of hominin paleontology and prehistoric archaeology is called paleoanthropology, human prehistory, or just prehistory—this article focuses on hominin paleontology. The data available for reconstructing human evolutionary history are genetic (from molecules) and phenotypic (from true and trace fossils). Genetic data include information about modern-human genetic variation that allows researchers to reconstruct the relatively recent migration of modern humans, plus ancient DNA that so far has been recovered from modern humans, Neanderthals, Denisovans, and the fossils from a site in Spain called the Sima de los Huesos. Phenotypic evidence, which is divided into macroscopic and microscopic, can be gathered from the surface of true fossils (i.e., bones and teeth) as well as from their internal structure. The latter can be accessed nondestructively by using imaging techniques or destructively by making sections of bones and teeth. The trace fossils that are most relevant for human evolution are footprints such as the c. 3.6-million-year-old hominin footprint trails from Laetoli in Tanzania.

General Overviews

The sources cited in this section are books or textbooks that cover human evolution. While they have that in common, their emphases are different. Aiello and Dean 1990 focuses on morphology, Klein 2009 on archaeology, Conroy and Pontzer 2012 on the fossil record, and Harcourt 2012 on what can be gleaned from living and recent modern humans. Wood 2011 includes entries that provide details of fossils, sites, and methods. Wood 2019 is an accessible summary.

History

The sources cited in this section are books or articles that cover human evolution from a historical perspective. Reader 2011 is an accessible account of the history of the discovery of the evidence for human evolution; Tattersall 2009 covers much of the same ground, but with different emphases. Frank Spencer’s history of physical anthropology (Spencer 1997) is more inclusive than just human evolution, but his scholarship is impressive. Matthew Goodrum is a trained historian of science, and he brings the rigor of that discipline to his three accounts; Goodrum 2013 is a summary, with Goodrum 2004a and Goodrum 2004b providing more historical detail. Corbey and Theunissen 1995 and Corbey 2005 provide important historical context about the history of our understanding of the great apes. Theunissen 1989 focuses on Eugène Dubois, one of the pioneers of human evolution research.

  • Corbey, R. 2005. The metaphysics of apes: Negotiating the animal-human boundary. Cambridge, UK: Cambridge Univ. Press.

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    A distinguished historian and philosopher summarizes the literature and presents his own views on the history and relationships of the apes.

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    • Corbey, R., and B. Theunissen, eds. 1995. Ape, man and apeman: Changing views since 1600. Cambridge, UK: Cambridge Univ. Press.

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      The contributors provide a comprehensive review of the history of the discovery, recognition, and interpretation of the living apes.

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      • Goodrum, M. R. 2004a. Prolegomenon to a history of paleoanthropology: The study of human origins as a scientific enterprise; Part 1, Antiquity to the eighteenth century. Evolutionary Anthropology: Issues, News, and Reviews 13.5: 172–180.

        DOI: 10.1002/evan.20029Save Citation »Export Citation »E-mail Citation »

        An authoritative review of the early attempts by modern humans to understand how they relate to the rest of the living world. It explores the history of the philosophical and scientific theories of human origins from ancient Greece and Rome up to when the Scientific Revolution led to a renewed interest in investigating human origins in a more scientific way. Available online by subscription.

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        • Goodrum, M. R. 2004b. Prolegomenon to a history of paleoanthropology: The study of human origins as a scientific enterprise; Part 2, Eighteenth to the twentieth century. Evolutionary Anthropology: Issues, News, and Reviews 13.6: 224–233.

          DOI: 10.1002/evan.20030Save Citation »Export Citation »E-mail Citation »

          An excellent summary of the later history of our awareness of, and research into, human evolution. It examines the role that geology, paleontology, biology, anthropology, and archaeology played during the period from 1700 to the mid-20th century in establishing a modern science of paleoanthropology. Reviews the major theories, hominid fossil discoveries, and debates that have shaped modern theories of human evolution. Available online by subscription.

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          • Goodrum, M. R. 2013. History. In A companion to paleoanthropology. Edited by D. R. Begun, 17–33. Blackwell Companions to Anthropology 22. Hoboken, NJ: Wiley-Blackwell.

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            An eminently readable and concise summary of the history of paleoanthropology.

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            • Reader, J. 2011. Missing links: In search of human origins. Updated ed. Oxford: Oxford Univ. Press.

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              John Reader is a photojournalist, but he is also a scholar of the history of human evolution and has a talent for capturing important events in that history in the form of photomontages.

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              • Spencer, F., ed. 1997. History of physical anthropology: An encyclopedia. 2 vols. Garland Reference Library of Social Science 677. New York: Garland.

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                This encyclopedia covers more ground than just human evolution, but it has many entries that provide a sound coverage of the history of the latter.

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                • Tattersall, I. 2009. The fossil trail: How we know what we think we know about human evolution. 2d ed. Oxford: Oxford Univ. Press.

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                  This well-written history of paleoanthropology is an updated version of a book first published in 1995.

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                  • Theunissen, B. 1989. Eugène Dubois and the ape-man from Java: The history of the first “missing link” and its discoverer. Dordrecht, The Netherlands: Kluwer.

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                    A noted historian of paleoanthropology explores Dubois’s crucial contributions to paleoanthropology.

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                    Journals

                    Announcements of important new fossil evidence are usually made in high-impact general science journals such as Nature, Science, Nature Ecology and Evolution, and the Proceedings of the National Academy of Sciences of the United States of America. The only journals that specialize in human evolution are the Journal of Human Evolution and Paleoanthropology. The American Journal of Physical Anthropology carries many articles that are relevant to human evolution. Evolutionary Anthropology: Issues, News, and Reviews is an excellent review journal that includes accessible and authoritative articles relevant to human evolution.

                    Comparative Context

                    Interest in the comparative context of modern humans dates back at least to Tyson 1699, but Huxley 1863 was the first publication to link this evidence with Charles Darwin’s insight that modern humans were more closely related to the living African great apes—the chimpanzee (bonobos were not recognized until much later) and gorilla—than they were to the only Asian great ape, the orangutan. The first indication of a particularly close relationship between modern humans and chimpanzees came from studies of hemoglobin (Zuckerkandl, et al. 1960; Zuckerkandl 1963), albumin (Goodman 1963), and other proteins (Sarich and Wilson 1967), but it has now been confirmed on the basis of sequence analyses of samples of great ape DNA.

                    • Goodman, M. 1963. Man’s place in the phylogeny of the primates as reflected in serum proteins. In Classification and human evolution. Edited by S. L. Washburn, 204–234. Viking Fund Publications in Anthropology 37. Chicago: Aldine.

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                      Goodman used immunodiffusion to study the affinities of albumin, one of the serum proteins, and showed that the albumins of modern humans and the chimpanzee are effectively identical.

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                      • Huxley, T. H. 1863. Evidence as to man’s place in nature. London: Williams and Norgate.

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                        Huxley’s book is a collection of three essays. The first reviews the history of discovery of the great apes and what was known about them in 1863. The second considers how Man (i.e., modern humans) is related to the rest of the animal kingdom, and the third reviews what little was known at the time about the fossil evidence for human evolution.

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                        • Sarich, V. M., and A. C. Wilson. 1967. Immunological time scale for hominid evolution. Science 158.3805: 1200–1203.

                          DOI: 10.1126/science.158.3805.1200Save Citation »Export Citation »E-mail Citation »

                          Sarich and Wilson exploited minor differences in the structure of protein molecules to infer the evolutionary history of the taxa to whom those protein molecules belong. Like Zuckerkandl and Goodman, they concluded that modern humans and the African apes, in particular the chimpanzee, are closely related. Available online by subscription.

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                          • Tyson, E. 1699. Orang-outang, sive, Homo sylvestris, or, The anatomy of a pygmie compared with that of a monkey, an ape, and a man. London: T. Bennet and D. Brown.

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                            A careful and detailed report of the soft- and hard-tissue anatomy of a juvenile chimpanzee, stressing the similarities and differences between its anatomy and that of modern humans.

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                            • Zuckerkandl, E. 1963. Perspectives in molecular anthropology. In Classification and human evolution. Edited by S. L. Washburn, 243–272. Chicago: Aldine.

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                              A useful review of the state of play when molecular anthropology was in its infancy.

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                              • Zuckerkandl, E., R. T. Jones, and L. Pauling. 1960. A comparison of animal hemoglobins by tryptic peptide pattern analysis. Proceedings of the National Academy of Sciences of the United States of America 46.10: 1349–1360.

                                DOI: 10.1073/pnas.46.10.1349Save Citation »Export Citation »E-mail Citation »

                                Zuckerkandl and colleagues used enzymes to break up the hemoglobin protein into its peptide components and showed that the peptides of modern humans, the gorilla, and the chimpanzee are indistinguishable.

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                                Great Ape Genome

                                The discovery of the significance of DNA took some time to have an impact on human evolution, but analyses of the genomes of the great apes are providing the comparative context for what is unique about the genome of modern humans. The first ape genome to be sequenced was that of the chimpanzee (Chimpanzee Sequencing and Analysis Consortium 2005), but it was not long before sequences were available for the orangutan (Locke, et al. 2011), gorilla (Scally, et al. 2012), and the bonobo (Prüfer, et al. 2012). Prado-Martinez, et al. 2013 reports the implications of analyzing the nuclear genomes of seventy-nine great apes. De Manuel, et al. 2016 provides more information about the genome of chimpanzees; Kronenberg, et al. 2018 suggests that a third of the modern human genome may be more similar to other great apes than to chimpanzees (also known as incomplete lineage sorting); and Moorjani, et al. 2016 pushes back the age of the common ancestor of modern humans and chimpanzees/bonobos. Kuhlwilm, et al. 2016 provides a recent general review, and Kuhlwilm, et al. 2019 reports genomic evidence of a third, extinct, Pan lineage that hybridized with bonobos after they split off from common chimpanzees.

                                Great Ape Phenome

                                It is ironic that we are better informed about the great ape genome than we are about the great ape phenome (i.e., phenotype). Huxley 1863, cited under Comparative Context, provides the first review, and it is only relatively recently that researchers are beginning to refocus on this topic (Diogo and Wood 2011; Diogo, et al. 2017).

                                Contextual Evidence

                                The value of a hominin fossil is markedly diminished if there is no information about its context (i.e., geological age, paleohabitat, contemporary fauna). Dating information enables fossils found at different sites to be related in time, and information about past climates and the paleoenvironment enables researchers to develop and test hypotheses about the adaptations of early hominins.

                                Dating

                                The umbrella term used for methods that can provide ages for fossils or rock layers is geochronology. Dating methods traditionally have been divided into two categories, absolute and relative, but researchers involved in dating have largely abandoned the absolute/relative dichotomy. Instead, geochronological methods are more usually classified on the basis of the type of method (e.g., isotopic, radiogenic, etc.) and how the results are expressed. For example, sidereal dating methods (e.g., dendrochronology) are based on counting annual events; isotopic dating methods (e.g., argon-argon dating, radiocarbon, etc.) measure changes in the absolute amounts or ratios of isotopes; radiogenic dating methods (e.g., electron spin resonance spectroscopy dating, fission track dating, etc.) rely on measuring the effects of radioactive decay; chemical dating methods (e.g., amino acid racemization) rely on measuring the progress of time-dependent processes; geomorphic dating methods (e.g., sedimentation rates) rely on processes that affect the landscape; and correlation dating methods (e.g., biostratigraphy, magnetostratigraphy, stratigraphy, tephrochronology) rely on matching evidence from the location being dated to sequences that, to varying degrees of precision, reflect the passage of time on a global or regional scale. Numerical-age dating methods (e.g., sidereal, isotopic, and radiogenic) express the age in years; calibrated-age and relative dating methods (e.g., chemical, biological, and geomorphic) provide approximations of the real age; and correlated-age dating methods (e.g., biostratigraphy, magnetostratigraphy, stratigraphy, tephrochronology) provide an age by relating the fossil or horizon being examined to another sequence that is dated independently. Noller, et al. 2000 and Colman and Pierce 2000 provide excellent reviews of the gamut of dating methods available, Deino 2013 focuses on the methods that are most applicable to dating the early hominin fossil record, and Brown and McDougall 2011 provide examples of how these methods have been applied to sites in the Omo-Turkana Basin.

                                • Brown, F. H., and I. McDougall. 2011. Geochronology of the Turkana depression of northern Kenya and southern Ethiopia. In Special issue: The Turkana Basin. Evolutionary Anthropology: Issues, News, and Reviews 20.6: 217–227.

                                  DOI: 10.1002/evan.20318Save Citation »Export Citation »E-mail Citation »

                                  A paper showing how a variety of dating methods are used to provide a chronological framework for the sites around the Omo-Turkana Basin. Available online by subscription.

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                                  • Colman, S. M., and K. L. Pierce. 2000. Classifications of Quaternary geochronologic methods. In Quaternary geochronology: Methods and applications. Edited by J. S. Noller, J. M. Sowers, and W. R. Lettis, 2–5. AGU Reference Shelf 4. Washington, DC: American Geophysical Union.

                                    DOI: 10.1029/RF004Save Citation »Export Citation »E-mail Citation »

                                    An introduction to the methods used to date the hominin fossil record and an explanation of one way they are classified.

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                                    • Deino, A. L. 2013. Geochronology. In A companion to paleoanthropology. Edited by D. R. Begun, 244–264. Blackwell Companions to Anthropology 22. Oxford: Wiley-Blackwell.

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                                      Concise review written by one of the most experienced researchers who work on the isotopic dating of fossil hominins.

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                                      • Noller, J. S., J. M. Sowers, and W. R. Lettis, eds. 2000. Quaternary geochronology: Methods and applications. AGU Reference Shelf 4. Washington, DC: American Geophysical Union.

                                        DOI: 10.1029/RF004Save Citation »Export Citation »E-mail Citation »

                                        Clearly written articles about many of the methods used to date fossil hominins.

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                                        Paleoclimate

                                        Hominin evolution has taken place at a time when there have been major changes in global climate. One way researchers study climate change is to use drilling machines to sample sediment from the ocean floor (also known as deep-sea cores). Microscopic organisms called foraminifera (usually shortened to “forams”) are suspended in the water of the world’s oceans. Foraminifera take up two forms of oxygen isotope, one of which (16O) is lighter than the other (18O). When the oceans are warmer, the lighter isotope evaporates at a higher rate than the heavier one, so researchers use the proportions of the two oxygen isotopes as a proxy for the temperature of the oceans, and they use ocean water temperature as a proxy for global climate. During the period from eight to five million years ago (Ma), the earth experienced the beginning of a long-term drying and cooling trend; early hominin evolution almost certainly took place in Africa at the time of these changes. Prior to c. 3 Ma, global climate was dominated by hotter/drier and cooler/wetter cycles that were 23,000 years (c. 23 ka) long. Around c. 3 Ma the periodicity of these cycles switched to c. 41 ka, and around c. 800 ka it switched yet again to being dominated by c. 100 ka-long cycles. These c. 100 ka cycles are responsible for the periods of intense cold recorded in the Northern Hemisphere during the past million years. Aside from their influence on climate, these cold periods had another important influence on human evolution because when so much water is locked up in the ice caps at the North and South Poles it is inevitable that the sea level will fall. This would have exposed much of the continental shelf, and it was these reductions in sea level that enabled modern human ancestors to migrate from the Old World both to the islands of Southeast Asia and on to Australasia and to the New World. Within any particular region, climate is the result of a complex interaction between global climate and local influences such as latitude, altitude, the presence of mountain ranges, etc. DeMenocal 1995 laid out the evidence for a link between orbital dynamics and paleoclimate, and deMenocal 2004 and deMenocal 2011 review the evidence for climate change in Africa during the period covered by human evolution. Zachos, et al. 2001 provides a perspective from deeper time about the relatively recent (<10 Ma) changes in climate; Levin 2015 explains how paleoclimate affects vegetation; and Feakins, et al. 2005 shows how plant waxes preserved in strata can be used to track orbitally paced changes in vegetation. Uno, et al. 2016 shows how plant waxes preserved in sediments in the floor of the ocean can be used to trace the expansion of grasslands in Africa.

                                        Paleoenvironment

                                        Just as the topography of the Earth’s surface is not the same as it was several million years ago, the environments in a region in the past were not necessarily the same as those of today. Researchers reconstruct past environments (also known as paleoenvironments) by using geological and paleontological evidence. Chemical analysis is used to tell whether a soil was laid down in moist or dry conditions, and paleontologists can tell a lot about hominin paleohabitats from the types of animals found along with the fossil hominins. They use both large mammals and small mammals (e.g., mice and gerbils) to reconstruct past environments. Small mammals (also known as micromammals) are a subset of a more inclusive category called microfauna. Microfauna are especially useful because their geographical ranges are smaller than those of larger animals (e.g., cheetahs), so they provide more geographically precise habitat reconstructions. The remains of animals preyed on by owls found in owl pellets are a useful source of microfauna. Researchers who use larger mammals such as primates to reconstruct past environments have to be careful not to assume that the habitat preferences of the ancestors were the same as their modern-day representatives. For example, although modern colobus monkeys are leaf eaters who live in dense woodland, researchers have found that their ancestors lived in more-open habitats, so the presence of colobus monkeys at a c. 5 Ma site does not mean the same as finding colobus monkeys in a location today. Vrba 1985 is one of the first works to provide a testable hypotheses about the link between climate and human evolution, and Bobe, et al. 2007; Kingston 2007; Sponheimer, et al. 2013; and Reed 2013 provide reviews of the methods used. Bobe 2011 and Cerling, et al. 2011 show how these methods can be applied to sites in the Omo-Turkana Basin.

                                        • Bobe, R. 2011. Fossil mammals and paleoenvironments in the Omo-Turkana Basin. In Special issue: The Turkana Basin. Evolutionary Anthropology: Issues, News, and Reviews 20.6: 254–263.

                                          DOI: 10.1002/evan.20330Save Citation »Export Citation »E-mail Citation »

                                          A case study of how faunal evidence can help reconstruct how paleoenvironmental changes across time and space in a large African lake basin. Available online for purchase or by subscription.

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                                          • Bobe, R., Z. Alemseged, and A. K. Behrensmeyer, eds. 2007. Hominin environments in the East African Pliocene: An assessment of the faunal evidence. Vertebrate Paleobiology and Paleoanthropology 1. Dordrecht, The Netherlands: Springer.

                                            DOI: 10.1007/978-1-4020-3098-7Save Citation »Export Citation »E-mail Citation »

                                            This volume contains reviews of the ways faunal evidence can help in the reconstruction of the paleoenvironments at African early hominin sites.

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                                            • Cerling, T. E., N. E. Levin, and B. H. Passey. 2011. Stable isotope ecology in the Omo-Turkana Basin. In Special issue: The Turkana Basin. Evolutionary Anthropology: Issues, News, and Reviews 20.6: 228–237.

                                              DOI: 10.1002/evan.20326Save Citation »Export Citation »E-mail Citation »

                                              The application of state-of-the-art stable isotope science to faunal evidence from the Omo-Turkana Basin. Available online for purchase or by subscription.

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                                              • Kingston, J. D. 2007. Shifting adaptive landscapes: Progress and challenges in reconstructing early hominid environments. In Special issue: Supplement; Yearbook of Physical Anthropology. Edited by Sarah Stinson. American Journal of Physical Anthropology 134.45: 20–58.

                                                DOI: 10.1002/ajpa.20733Save Citation »Export Citation »E-mail Citation »

                                                Excellent review of what can, and what cannot, be deduced about the environments that are sampled at early hominin fossil sites.

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                                                • Reed, K. E. 2013. Multiproxy paleoecology: Reconstructing evolutionary context in paleoanthropology. In A companion to paleoanthropology. Edited by D. R. Begun, 203–225. Blackwell Companions to Anthropology 22. Oxford: Wiley-Blackwell.

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                                                  This review focuses on methods for reconstructing paleohabitats that can be applied to hominin sites.

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                                                  • Sponheimer, M., J. A. Lee-Thorp, K. E. Reed, and P. S. Ungar, eds. 2013. Early hominin paleoecology. Boulder: Univ. Press of Colorado.

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                                                    A review of the different lines of evidence that can be brought to bear on reconstructing the environments of early hominins.

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                                                    • Vrba, E. S. 1985. Ecological and adaptive changes associated with early hominid evolution. In Ancestors: The hard evidence. Edited by E. Delson, 63–71. New York: Alan R. Liss.

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                                                      One of the first papers to link the human fossil record and evidence about the evolution of non-hominins with emerging evidence about paleoclimates.

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                                                      Methods

                                                      The discovery of a hominin fossil is seldom a random event, because fossil sites occur in predictable locations. The fossils recovered are seldom, if ever, a random sample of the populations that lived in the past, and in this section we review the methods used to account for these biases. Only rarely are fossils complete and undamaged, so we also review the methods used to reassemble and reconstruct fossil evidence. Shape and size are the key elements of the morphology of any fossil, be it large or small, and we review the main methods used to capture morphology and then analyze it to generate taxonomic and other types of hypothesis.

                                                      Discovery

                                                      Paleoanthropologists look for fossils where rocks of the right age, say, back to eight million years old (8 Ma) have been exposed by natural erosion. Erosion occurs in places where streams and rivers cut through rock layers. This is especially likely to have occurred in regions where the Earth’s crust has been buckled and cracked as large landmasses, called tectonic plates, are pushed together. The floors and walls of rift valleys are formed when the Earth’s crust shears at cracks, or faults, where on one side the crust is forced upward and on the other, it moves downward. Sediments are exposed on the sides and floors of the valleys that form when streams and rivers erode their way through the blocks of sediment that are thrown up or down at such faults. Places on these exposed sediments (also known as exposures) where fossils are concentrated are called localities. Some fossil sites (e.g., Koobi Fora, Middle Awash) cover large areas and include many localities, while others are much smaller and may only have one, or a few, localities. Hominin fossils are also found in the sediments that form in caves. Caves can be formed on the coast by erosion, but most early hominin fossils come from caves that formed when rain percolated through cracks in limestone. Cracks become cavities, and when these cavities communicate with the surface, soil and the remains of animals enter the cave. Later in the fossil record hominins used caves for shelter, but most early hominin fossils found in caves belong to individuals whose remains fell in, or were washed into, the cave, or in the case where much of a single skeleton is preserved, to individual hominins who may have found the caves easier to enter than to leave. Rarely, hominin fossils are discovered in museum collections. This happens either when researchers initially did not realize a fossil belonged to a hominin, or when fossils are lost or misidentified when they are moved from one museum or laboratory to another. Brain 1981 reviews the formation of the southern African hominin cave sites, and Brain 2004 focuses on one of the best-known sites, Swartkrans. Behrensmeyer, et al. 2002; Quade and Wynn 2008; and Feibel 2011 review the geological context of the main East Africa sites. Maureille 2002 recounts how detective work enabled an important hominin fossil to be recovered from a museum where it had been stored with stone tools.

                                                      • Behrensmeyer, A. K., R. Potts, A. Deino, and P. W. Ditchfield. 2002. Olorgesailie, Kenya: A million years in the life of a rift basin. In Sedimentation in continental rifts. Edited by R. W. Renaut and G. M. Ashley, 97–106. Special Publication 73. Tulsa, OK: Society for Sedimentary Geology.

                                                        DOI: 10.2110/pec.02.73Save Citation »Export Citation »E-mail Citation »

                                                        An excellent general introduction to the circumstances that surround the accumulation of hominin fossils at some of the main East African hominin sites (e.g., Olduvai, Koobi Fora, Hadar).

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                                                        • Brain, C. K. 1981. The hunters or the hunted? An introduction to African cave taphonomy. Chicago: Univ. of Chicago Press.

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                                                          A classic survey of the factors that determine how fossils become incorporated in the sediments found in the southern African hominin cave sites.

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                                                          • Brain, C. K., ed. 2004. Swartkrans: A cave’s chronicle of early man. 2d ed. Transvaal Museum Monograph 8. Pretoria, South Africa: Transvaal Museum.

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                                                            The second edition of a meticulous description of Swartkrans, which is the best understood of the southern African hominin cave site in terms of how, and in what sequence, the sediments and hominin fossils entered the caves.

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                                                            • Feibel, C. S. 2011. A geological history of the Turkana Basin. In Special issue: The Turkana Basin. Evolutionary Anthropology: Issues, News, and Reviews 20.6: 206–216.

                                                              DOI: 10.1002/evan.20331Save Citation »Export Citation »E-mail Citation »

                                                              A summary of the geological context of the hominin sites (e.g., Koobi Fora, West Turkana) in the Omo-Turkana Basin. Available online for purchase or by subscription.

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                                                              • Maureille, B. 2002. A lost Neanderthal neonate found. Nature 419.6902: 33–34.

                                                                DOI: 10.1038/419033aSave Citation »Export Citation »E-mail Citation »

                                                                The skeleton of a Neanderthal baby from the site of Le Moustier was sent to Marcellin Boule for an assessment of its age. All trace of the skeleton seemed to have been lost until a researcher found the bones of a neonate among the stone tools from the site of Les Eyzies. Available online by subscription.

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                                                                • Quade, J., and J. G. Wynn. 2008. The geology of early humans in the Horn of Africa. Papers presented at a topical session of the 2004 Geological Society of America Annual Meeting, held in Denver, Colorado, 7–10 November 2004. Geological Society of America, Special Papers 446. Boulder, CO: Geological Society of America.

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                                                                  This volume contains papers that summarize the geological context of the fossil evidence of archaic hominins recovered from the Ethiopian sites of Dikika, Gona, Hadar, and Ledi-Geraru. Available online by subscription.

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                                                                  Detecting and Correcting for Bias

                                                                  Taphonomy refers to the subdiscipline of science that investigates the factors involved in the death, decay, preservation, and fossilization of organisms. Taphonomists study the transition of organic materials from the biosphere to being part of the geological record (also known as lithosphere). It is only relatively recently that scientists have taken an interest in the range of processes that convert a once-living community into its fossil record. For a long time it was assumed that fossils found at a site were an unbiased sample of the animals living in the past, but we now know that some organisms are more likely to fossilize than others (differential survivorship), and some parts of an organism are more likely to be preserved than others (differential preservation). For example, with respect to differential survivorship, animals that go to waterholes to drink or to the lakeshore to graze are vulnerable to predators, and in both places their carcasses and bones are likely to be protected by sediments deposited by streams and rising lake levels. These two factors increase the likelihood that such animals will become part of the fossil record, whereas animals that live in more arid habitats away from sources of standing water are less likely to become part of the record. So, just because the remains of mammals adapted to arid habitats are few and far between in the fossil record, this does not mean these animals were few and far between in the mammalian paleocommunity sampled by that fossil record, nor that these habitats did not exist. An example of differential preservation is that teeth and dense bones are more likely to survive trampling and other sorts of damage than the more fragile bones of the skeleton. Another type of bias is that large animals tend to be better represented in the fossil record than smaller ones. By understanding the factors that bias the fossil record, allowance can be made for these factors when interpreting the hominin and non-hominin fossil records. Behrensmeyer and Hill 1980 and Behrensmeyer 1991 provide technical summaries of the principles and practice of taphonomy; Shipman 1981 and Marean 1995 provide accessible presentations for the nonexpert. Behrensmeyer 1993 uses the author’s classic research at Amboseli to explain taphonomy, and Soligo and Andrews 2005 focuses on the role taphonomy can play in improving our understanding of the hominin fossil record.

                                                                  • Behrensmeyer, A. K. 1991. Terrestrial vertebrate accumulations. In Taphonomy: Releasing the data locked in the fossil record. Edited by P. A. Allison and D. E. G. Briggs, 291–335. Topics in Geobiology 9. New York: Plenum.

                                                                    DOI: 10.1007/978-1-4899-5034-5_6Save Citation »Export Citation »E-mail Citation »

                                                                    An excellent summary of taphonomy.

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                                                                    • Behrensmeyer, A. K. 1993. The bones of Amboseli: Bone assemblages and ecological change in a modern African ecosystem. National Geographic Research 9.4: 402–421.

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                                                                      A classic study that uses the modern ecosystem of Amboseli as a laboratory to understand what is likely to have happened to the carcasses of hominins and other mammals in the past.

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                                                                      • Behrensmeyer, A. K., and A. P. Hill, eds. 1980. Fossils in the making: Vertebrate taphonomy and paleoecology. Papers presented at a symposium in July 1976 at Burg-Wartenstein, Austria, sponsored by the Wenner-Gren Foundation for Anthropological Research. Prehistoric Archeology and Ecology. Chicago: Univ. of Chicago Press.

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                                                                        A conference held in 1976 brought together nearly all of the scientists then active in taphonomy research. The article by Everett Olson (pp. 5–19) and the concluding summary by the editors (pp. 299–305) make particularly worthwhile reading. This volume is an excellent introduction to the principles and practice of taphonomy.

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                                                                        • Marean, C. W. 1995. Of taphonomy and zooarcheology. Evolutionary Anthropology: Issues, News, and Reviews 4.2: 64–72.

                                                                          DOI: 10.1002/evan.1360040209Save Citation »Export Citation »E-mail Citation »

                                                                          This extended review of R. Lee Lyman’s Vertebrate Taphonomy (Cambridge, UK: Cambridge Univ. Press, 1994) provides a clear and readable introduction to taphonomy. Available online for purchase or by subscription.

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                                                                          • Shipman, P. 1981. Life history of a fossil: An introduction to taphonomy and paleoecology. Cambridge, MA: Harvard Univ. Press.

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                                                                            A book-length presentation of taphonomy for the nonexpert.

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                                                                            • Soligo, C., and P. Andrews. 2005. Taphonomic bias, taxonomic bias and historical non-equivalence of faunal structure in early hominin localities. Journal of Human Evolution 49.2: 206–229.

                                                                              DOI: 10.1016/j.jhevol.2005.03.006Save Citation »Export Citation »E-mail Citation »

                                                                              The implications of taphonomic bias for interpreting the hominin fossil record. Available online by subscription.

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                                                                              Reassembly and Reconstruction

                                                                              Bones and teeth that are unaffected by plastic deformation can be reassembled. Until recently, researchers sat down with the original pieces and painstakingly tried to fit them together by hand, much like completing a very complicated 3-D jigsaw puzzle. More recently, researchers have been using CT scanning and computer software to create virtual fossils, the fragments of which can be moved and rotated on the screen. If a substantial part of an undistorted fossil bone or tooth has been preserved, researchers sometimes use it to reconstruct what the whole bone or tooth would have looked like. Reconstruction may involve duplication if the missing piece is part of a bilateral structure and the other side (also known as antimere) is preserved. Obviously, if there is no antimere and if only a small part of the whole structure is preserved, the less likely the reconstruction will resemble the intact bone or tooth. The more complete a bone or tooth is, and the more contact points there are between the fragments, the more reliable the reconstruction. Bones can be plastically deformed either before they are fossilized or before fossilization has substantially hardened and stiffened them. The real problems occur when a fossil is both incomplete and fragmented, and it has been affected by plastic deformation. Postmortem modifications to bones and teeth can occur before, during, and after fossilization. If a bone or tooth is subjected to wind or water erosion, it may lose its surface bone and thus be smaller than it was during life. If a bone or tooth is subjected to heating during the day and cooling at night, it may crack, and if it is then covered by a fine sediment or a sandy soil, the sediment or soil may enter the cracks and eventually form a hard matrix. Unlike the effects of erosion, matrix-filled cracks exaggerate the size and may distort the shape of the fossil compared to its size and shape at the time of death. Matrix-filled cracking is very difficult to correct on the fossils themselves, but modern imaging techniques now make it possible for researchers to use software programs to discriminate between bone and matrix. These programs can then be used to virtually remove the matrix from a fossil affected by matrix-filled cracking, and then, if the bone fragments themselves have not been distorted, the same programs can be used to virtually reassemble the fossil. Zollikofer, et al. 1998 sets out the principles of virtual reconstruction, and Zollikofer, et al. 2005 applies those principles to the reconstruction of a cranium that is 7 Ma old.

                                                                              Data Capture

                                                                              Once a hominin bone or tooth, against all the odds, has been fossilized and then discovered either lying on the ground (also known as surface find) or uncovered during an excavation (also known as in situ discovery), how is it analyzed? First, the fossil needs to be compared with other hominin fossils and with the appropriate extant taxa. The physical characteristics of the fossil and the comparators need to be captured as comprehensively, and with as little subjectivity and as much objectivity (i.e., the methods used must give results that can be replicated by other researchers), as possible. The external and internal morphology of a fossil can be usefully divided into macroscopic (morphology that can be seen with the naked eye) or microscopic (morphology that can be seen only with the aid of a microscope). Information about internal morphology can be obtained destructively or nondestructively. Nondestructive techniques involve one or other types of imaging modality (e.g., Ohman, et al. 1997; Spoor, et al. 2000; Bromage, et al. 2005). Destructive techniques usually involve some form of physically sectioning (or slicing) the fossil (e.g., Dean, et al. 1993). Two systems of recording morphology are in use. One uses measurements and the other records morphology more subjectively by using presence/absence criteria or by comparing the morphology of the fossil with a series of standards. Traditional measurements are made between standardized locations on bones and teeth, but most contemporary techniques record the shape of an object in three dimensions and then analyze those data using 3-D geometric morphometric methods (e.g., O’Higgins 2000).

                                                                              Data Analysis

                                                                              Measurements can be compared one at a time in a univariate analysis, two at a time when they are plotted against each other in a bivariate analysis, and many variables can be analyzed simultaneously in a multivariate analysis (e.g., Oxnard 1973, Albrecht 1978). The latter methods are used to compare fossils with individuals from known groups, by summarizing many variables in the form of a smaller number of factors or canonical variates. Researchers can then locate the fossil in multivariate space and then measure the distance between fossils, or between the fossil and various comparative samples. Other multivariate methods (e.g., principal components analysis) simplify patterns of correlation and variance to identify clusters of similar fossils. Another subgroup of multivariate methods enables a complex structure such as a fossil bone or tooth to be broken down into its size and shape components. Conventional multivariate techniques provide no visual image of how organisms differ in shape, but a new generation of geometric morphometric methods use a system of grids and arrows to show how the reference specimen would need to be deformed (also known as warped) in order to assume the shapes of the specimens with which it is being compared. Nunn 2011 and Schillaci and Gunz 2013 provide summaries of multivariate methods.

                                                                              • Albrecht, G. H. 1978. The craniofacial morphology of the Sulawesi macaques: Multivariate approaches to biological problems. Edited by F. S. Szalay. Contributions to Primatology 13. Basel, Switzerland: Karger.

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                                                                                Albrecht explains how the multivariate analytical methods covered in Oxnard 1973 are applied to an extant data set.

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                                                                                • Nunn, C. L. 2011. The comparative approach in evolutionary anthropology and biology. Chicago: Univ. of Chicago Press.

                                                                                  DOI: 10.7208/chicago/9780226090009.001.0001Save Citation »Export Citation »E-mail Citation »

                                                                                  The types of modern quantitative methods that are being applied to the analysis of fossil hominins.

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                                                                                  • Oxnard, C. E. 1973. Form and pattern in human evolution: Some mathematical, physical, and engineering approaches. Chicago: Univ. of Chicago Press.

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                                                                                    Oxnard, who was a pioneer of multivariate methods both for taxonomy and functional analysis, explains the principles of multivariate analysis.

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                                                                                    • Schillaci, M. A., and P. Gunz. 2013. Multivariate quantitative methods in paleoanthropology. In A companion to paleoanthropology. Edited by D. R. Begun, 75–96. Blackwell Companions to Anthropology 22. Oxford: Wiley-Blackwell.

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                                                                                      A review of multivariate quantitative methods for the nonspecialist.

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                                                                                      Taxonomy

                                                                                      The process of allocating individual fossil specimens (e.g., the equivalent of an individual automobile) to a group (e.g., 2019 model of the Subaru Forester), assigning the groups to categories (e.g., sport utility vehicles), and then arranging the groups in a hierarchy of increasingly inclusive categories is called classification. Systematics refers to the theory and the practice of classification. The process of classification begins with identification, which is the act of allocating individual specimens (e.g., the automobile belonging to your neighbor) to a group. If a newly recovered fossil specimen is within the inferred limits of variation of an existing taxon (e.g., your neighbor’s car conforms to the specifications of 2019 Subaru Foresters), then all is well and good. However, if the specimen falls outside the scope of any previously recognized taxon, it may warrant recognizing a new taxon. The new taxon has to be given an appropriate name, a type specimen needs to be designated, and it must be found a place in the existing taxonomic scheme or the existing taxonomy needs to be modified to accommodate it. The steps involved in naming a new taxon are collectively referred to as nomenclature, and the process is controlled by rules and recommendations set out in the International Code of Zoological Nomenclature (also known as ICZN or just “the Code”). Wood 2010 takes the reader through the steps involved in processing a hominin fossil.

                                                                                      • Wood, B. A. 2010. Systematics, taxonomy, and phylogenetics: Ordering life, past and present. In A companion to biological anthropology. Edited by C. S. Larsen, 56–73. Blackwell Companions to Anthropology 7. Malden, MA: Wiley-Blackwell.

                                                                                        DOI: 10.1002/9781444320039Save Citation »Export Citation »E-mail Citation »

                                                                                        How an individual fossil is analyzed to see if it belongs to an existing hominin taxon.

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                                                                                        Phylogeny Reconstruction

                                                                                        Once the fossil record has been resolved into species, the next task is to understand how those species are related. Was there just a single hominin lineage, or does the hominin clade consist of several lineages, each with its own unique morphological signature? This problem has been addressed, apparently successfully, at higher taxonomic levels (i.e., the relationships between major groupings such as birds and reptiles) by a method called cladistics, or phylogenetic analysis. But it is not clear how successful cladistics is at determining the phylogenetic significance of the relatively subtle differences among hominin species, especially when the fossil record of early hominins is sparse and is dominated by skulls and teeth. Smith 1994 and Lemey, et al. 2009 provide general reviews of cladistic methods, and Wood 2010 and Strait 2013 explain the problems and pitfalls of applying these methods to the hominin fossil record.

                                                                                        Hominin Taxonomy

                                                                                        The hominin fossil record can be broken down into grades or clades. The former emphasizes what type of animal it is, the latter focuses on its phylogenetic history. Hypotheses about grades are generally, but not always, more robust than hypotheses about clades, so in this section’s subsections, widely recognized hominin fossil taxa have been broken down into five inclusive grades, Possible and Probable Hominins, Archaic Hominins, Transitional Hominins, Premodern Homo, and Anatomically Modern Humans. Wood 2010 provides an overview of the hominin fossil record and explains the concept of clades. Simpson 2013 reviews the taxa that have been proposed as being ancestral to all later hominins; MacLatchy, et al. 2010 reviews the fossil evidence for early hominins in Africa; and Rightmire 2010 surveys the origins and evolution of the genus Homo.

                                                                                        Possible and Probable Hominins

                                                                                        When the principles of neutral mutation are applied to the molecular differences between modern humans and chimpanzees/bonobos, they suggest that the common ancestor of these two groups would have been living between about twelve and five million years ago, with most estimates tending to be closer to the younger end of the range (i.e., 8–6 Ma). The common ancestor of later hominins was almost certainly more ape-like than modern human–like, but it was unlikely to have been like any modern ape. Discoveries made at Aramis in Ethiopia in the 1990s that are c. 4.4 Ma and that display an intriguing mixture of features, some of which had formerly had been regarded as peculiar to Australopithecus or as ape-like, were allocated to a novel species and placed in a new genus as Ardipithecus ramidus (White, et al. 1994; White, et al. 2009; Lovejoy, et al. 2009; Simpson, et al. 2019). Subsequent discoveries at localities older than Aramis were referred to a second species of Ardipithecus, as Ardipithecus kadabba (c. 5.7 Ma) (Haile-Selassie 2001; Haile-Selassie, et al. 2004). Hominin-like fossils from the site of Lukeino in Kenya, dated to c. 6 Ma, were placed in a different genus, as Orrorin tugenensis (Senut, et al. 2001), and fossils dating to c. 7 Ma discovered at a site called Toros-Menalla in Chad in central Africa were assigned to yet another new genus, as Sahelanthropus tchadensis (Brunet, et al. 2002; Brunet, et al. 2005). All of these taxa, at one time or another, have been put forward as the likely ancestor of all later hominins. But, how certain can we be that any of these discoveries sample taxa that are more closely related to modern humans than to chimpanzees/bonobos? Could they be ancestors of living chimpanzees, or belong to an archaic “proto-hominin” group with no direct link to either living chimpanzees/bonobos or to modern humans (Wood and Harrison 2011)?

                                                                                        • Brunet, M., F. Guy, D. Pilbeam, et al. 2002. A new hominid from the Upper Miocene of Chad, Central Africa. Nature 418.6894: 145–151.

                                                                                          DOI: 10.1038/nature00879Save Citation »Export Citation »E-mail Citation »

                                                                                          The announcement of six fossils, including an adult cranium (TM 266-01-060-1) and part of a mandible, recovered in 2001 from a single locality, TM 266, in the Anthracotheriid Unit at Toros-Menalla in Chad, Central Africa. This paper diagnoses a new genus and species, Sahelanthropus tchadensis, with the adult cranium (TM 266-01-060-1) as its holotype. Available online by subscription.

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                                                                                          • Brunet, M., F. Guy, D. Pilbeam, et al. 2005. New material of the earliest hominid from the Upper Miocene of Chad. Nature 434.7034: 752–755.

                                                                                            DOI: 10.1038/nature03392Save Citation »Export Citation »E-mail Citation »

                                                                                            Additional fossils assigned to Sahelanthropus tchadensis were recovered in 2001 and 2002. The specimens included an upper premolar tooth from TM 266, and mandibles (TM 247-01-02 and TM 292-02-01) from two new localities. This additional evidence means that a minimum of six and a maximum of nine individuals are known from the Toros-Menalla region of Chad.

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                                                                                            • Haile-Selassie, Y. 2001. Late Miocene hominids from the Middle Awash, Ethiopia. Nature 412.6843: 178–181.

                                                                                              DOI: 10.1038/35084063Save Citation »Export Citation »E-mail Citation »

                                                                                              A report of eleven specimens (six postcranial and five dental) recovered in 1997 and thereafter from five Middle Awash localities that range in age from greater than 5.7 to 5.2 Ma. Initially, the specimens were allocated to a subspecies of Ardipithecus ramidus (see White, et al. 1994), as Ardipithecus ramidus kadabba, but in 2004 the authors switched to recognize it as a separate species, Ardipithecus kadabba. Available online by subscription.

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                                                                                              • Haile-Selassie, Y., G. Suwa, and T. D. White. 2004. Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution. Science 303.5663: 1503–1505.

                                                                                                DOI: 10.1126/science.1092978Save Citation »Export Citation »E-mail Citation »

                                                                                                Six teeth, including an upper canine and a third premolar, were recovered in 2002 from sediments dated to between 5.8 and 5.6 Ma. This additional evidence convinced Haile-Selassie and his colleagues that the enlarged hypodigm of Ardipithecus ramidus kadabba was distinct enough to be recognized as a separate hominin species, Ardipithecus kadabba. Available online by subscription.

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                                                                                                • Lovejoy, C. O., G. Suwa, S. W. Simpson, et al. 2009. The great divides: Ardipithecus ramidus reveals the postcrania of our last common ancestors with African apes. Science 326.5949: 100–106.

                                                                                                  DOI: 10.1126/science.1175833Save Citation »Export Citation »E-mail Citation »

                                                                                                  These authors suggest that Ardipithecus ramidus was more upright and bipedal than living apes. It interprets the ARA-VP-6/500 individual as weighing about fifty kilograms, and it suggests that it was adapted to walk on branches. Available online by subscription.

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                                                                                                  • Senut, B., M. Pickford, D. Gommery, et al. 2001. First hominid from the Miocene (Lukeino Formation, Kenya). Comptes Rendus de l’Académie des Sciences, Ser. IIa: Earth and Planetary Science 332.2: 137–144.

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                                                                                                    These authors make the case that c. 6 Ma fossils from four localities in the Lukeino Formation, in the Tugen Hills, in Kenya, that they assign to a new genus and species, Orrorin tugenensis, are the best evidence we have of a primitive hominin. Available online for purchase or by subscription.

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                                                                                                    • Simpson, S. W., N. E. Levin, J. Quade, et al. 2019. Ardipithecus ramidus postcrania from the Gona Project area, Afar Regional State, Ethiopia. Journal of Human Evolution 129:1–45.

                                                                                                      DOI: 10.1016/j.jhevol.2018.12.005Save Citation »Export Citation »E-mail Citation »

                                                                                                      The authors describe a fragmentary associated skeleton, some hand bones and a foot bone, they claim strengthens the case that Ardipithecus ramidus was more upright and bipedal than living apes. Available online by subscription.

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                                                                                                      • White, T. D., B. Asfaw, Y. Beyene, et al. 2009. Ardipithecus ramidus and the paleobiology of early hominids. Science 326.5949: 75–86.

                                                                                                        DOI: 10.1126/science.1175802Save Citation »Export Citation »E-mail Citation »

                                                                                                        This paper summarizes eleven papers published in Science in 2009 that focus on an extraordinarily complete associated skeleton of Ardipithecus ramidus (ARA-VP-6/500) recovered from Aramis, in the Middle Awash region of Ethiopia. The authors are adamant that Ar. ramidus is not an ape, but belongs at the base of the hominin clade. Available online by subscription.

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                                                                                                        • White, T. D., G. Suwa, and B. Asfaw. 1994. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature 371.6495: 306–312.

                                                                                                          DOI: 10.1038/371306a0Save Citation »Export Citation »E-mail Citation »

                                                                                                          A report of c. 4.4 Ma fossil evidence recovered from Aramis in the Middle Awash region of Ethiopia. It was initially assigned to a new species as Australopithecus ramidus, but a year later the same authors assigned it to a novel genus as Ardipithecus ramidus (errata published in 1995 in Nature 375.6526: 88). Available online by subscription.

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                                                                                                          • Wood, B., and T. Harrison. 2011. The evolutionary context of the first hominins. Nature 470.7334: 347–352.

                                                                                                            DOI: 10.1038/nature09709Save Citation »Export Citation »E-mail Citation »

                                                                                                            These authors look at the evidence for Ardipithecus ramidus from a broader perspective and suggest that this taxon is at least as likely to belong to an extinct clade as it is to be a primitive member of the hominin clade. Available online by subscription.

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                                                                                                            Archaic Hominins

                                                                                                            Archaic hominins are known from sites in three regions of Africa. In East and Central Africa, they are found at open-air sites. In southern Africa, hominin fossils are found at cave sites.

                                                                                                            Archaic Hominins from East and Central Africa

                                                                                                            Discoveries in East Africa, most of them made since the early 1990s, together with material from a site in Central Africa, make up the evidence for at least one, and perhaps several, species of Australopithecus as well as a single species of Kenyanthropus (Leakey, et al. 2001). In terms of the quality and quantity of the fossil record, the best-known East African Australopithecus species is Australopithecus afarensis, which has a fossil record that is as good as that for any early hominin (Johanson, et al. 1978; Alemseged, et al. 2006; Kimbel and Delezene 2009). Thus, it offers an opportunity to provide answers to the following questions: How reliably and precisely is it dated? How well can it be characterized in terms of its functional abilities? How different in size and shape are the skeletons of males and females? Does it display any evolutionary trends through time? Can its paleohabitat be determined? How do the other East and Central African archaic hominins, Australopithecus anamensis (Leakey, et al. 1995; Leakey, et al. 1998), Australopithecus garhi (Asfaw, et al. 1999), and Australopithecus bahrelghazali (Brunet, et al. 1995) differ from Au. afarensis? Are Au. anamensis and Au. afarensis time-successive species in a single lineage (Kimbel, et al. 2006; Haile-Selassie, et al. 2010)? Why did researchers decide to erect a new genus and species, Kenyanthropus platyops, for discoveries in Kenya instead of allocating them to Au. afarensis? Finally, what are the relationships of Au. garhi?

                                                                                                            • Alemseged, Z., F. Spoor, W. H. Kimbel, et al. 2006. A juvenile early hominin skeleton from Dikika, Ethiopia. Nature 443.7109: 296–301.

                                                                                                              DOI: 10.1038/nature05047Save Citation »Export Citation »E-mail Citation »

                                                                                                              This c. 3.35 Ma, nearly complete Australopithecus afarensis juvenile skeleton, DIK-1-1, was recovered from locality DIK-1 in the Dikika study area, which is adjacent to Hadar in the Afar region of Ethiopia. Available online by subscription.

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                                                                                                              • Asfaw, B., T. White, O. Lovejoy, B. Latimer, S. Simpson, and G. Suwa. 1999. Australopithecus garhi: A new species of early hominid from Ethiopia. Science 284.5414: 629–635.

                                                                                                                DOI: 10.1126/science.284.5414.629Save Citation »Export Citation »E-mail Citation »

                                                                                                                Asfaw and colleagues set out the evidence for a hominin with a novel combination of very large postcanine teeth and a primitive cranium. Available online by subscription.

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                                                                                                                • Brunet, M., A. Beauvilain, Y. Coppens, E. Heintz, A. H. E. Moutaye, and D. Pilbeam. 1995. The first australopithecine 2,500 kilometres west of the Rift Valley (Chad). Nature 378.6554: 273–275.

                                                                                                                  DOI: 10.1038/378273a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                  Three-and-a-half-million-year-old hominin remains collected in Chad, in Central Africa, were assigned to a new taxon, Australopithecus bahrelghazali. But the case for these remains being distinct from Australopithecus afarensis is not a strong one, and it is more likely that the Au. bahrelghazali hypodigm is a geographical variant of Au. afarensis. Available online by subscription.

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                                                                                                                  • Haile-Selassie, Y., B. Z. Saylor, A. Deino, M. Alene, and B. M. Latimer. 2010. New hominid fossils from Woranso-Mille (Central Afar, Ethiopia) and taxonomy of early Australopithecus. American Journal of Physical Anthropology 141.3: 406–417.

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                                                                                                                    The morphology and age of recent discoveries from the Woronso-Mille study area in Ethiopia are consistent with the hypothesis that Australopithecus anamensis and Australopithecus afarensis are most likely time-successive taxa within a single lineage, with the Laetoli hypodigm intermediate between Au. anamensis and the Hadar hypodigm of Au. afarensis (see Kimbel, et al. 2006). Available online for purchase or by subscription.

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                                                                                                                    • Johanson, D. C., T. D. White, and Y. Coppens. 1978. A new species of the genus Australopithecus (Primates: Hominidae) from the Pliocene of Eastern Africa. Kirtlandia 28:1–14.

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                                                                                                                      Johanson and colleagues made the case that hominin fossils recovered from Laetoli, in Tanzania, and from the Ethiopian site of Hadar, are distinct from Australopithecus africanus. They named the new taxon Australopithecus afarensis. The fossil evidence from Laetoli is modest compared to that from Hadar, but the type specimen, or holotype (the LH 4 mandible), is from Laetoli.

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                                                                                                                      • Kimbel, W. H., and L. K. Delezene. 2009. “Lucy” redux: A review of research on Australopithecus afarensis. Yearbook of Physical Anthropology 52:2–48.

                                                                                                                        DOI: 10.1002/ajpa.21183Save Citation »Export Citation »E-mail Citation »

                                                                                                                        A comprehensive review of the fossil evidence for Australopithecus afarensis, and the history of its interpretation.

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                                                                                                                        • Kimbel, W. H., C. A. Lockwood, C. V. Ward, M. G. Leakey, Y. Rak, and D. C. Johanson. 2006. Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record. Journal of Human Evolution 51.2: 134–152.

                                                                                                                          DOI: 10.1016/j.jhevol.2006.02.003Save Citation »Export Citation »E-mail Citation »

                                                                                                                          Researchers familiar with the fossil evidence suggest that Australopithecus anamensis and Australopithecus afarensis are most likely time-successive taxa within a single lineage, with the Laetoli hypodigm intermediate between Au. anamensis and the Hadar hypodigm of Au. afarensis. The morphology and age of recent discoveries from the Woronso-Mille study area in Ethiopia (see Haile-Selassie, et al. 2010) are consistent with this hypothesis. Available online by subscription.

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                                                                                                                          • Leakey, M. G., C. S. Feibel, I. McDougall, and A. Walker. 1995. New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya. Nature 376.6541: 565–571.

                                                                                                                            DOI: 10.1038/376565a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                            Fossils dating to between 4.5 and 4.2 Ma found at Kanapoi and Allia Bay in northern Kenya were placed in a new species, Australopithecus anamensis, because they were considered to be more apelike than Australopithecus afarensis. Available online by subscription.

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                                                                                                                            • Leakey, M. G., C. S. Feibel, I. McDougall, C. Ward, and A. Walker. 1998. New specimens and confirmation of an early age for Australopithecus anamensis. Nature 393.6680: 62–66.

                                                                                                                              DOI: 10.1038/29972Save Citation »Export Citation »E-mail Citation »

                                                                                                                              Report of additional evidence of Australopithecus anamensis from Kanapoi and Allia Bay in Kenya. Available online by subscription.

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                                                                                                                              • Leakey, M. G., F. Spoor, F. H. Brown, et al. 2001. New hominin genus from Eastern Africa shows diverse Middle Pliocene lineages. Nature 410.6827: 433–440.

                                                                                                                                DOI: 10.1038/35068500Save Citation »Export Citation »E-mail Citation »

                                                                                                                                Meave Leakey and her colleagues propose that a 3.5 Ma cranium (KNM-WT 40000) and a 3.3 Ma maxilla (KNM-WT 38350) from West Turkana are respectively the holotype and the paratype of Kenyanthropus platyops, a distinctly different hominin taxon that overlaps Australopithecus afarensis in time and probably space. Available online by subscription.

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                                                                                                                                Hyper-megadont Archaic Hominins from East Africa

                                                                                                                                Hominins from East Africa with very large premolar and molar crowns (other than Australopithecus garhi—see Archaic Hominins from East and Central Africa) are assigned to two taxa. The earlier one, Paranthropus aethiopicus, retains large anterior teeth and a more projecting face, whereas the later one, Paranthropus boisei, has small anterior teeth and a tall and flat face. Both have a large, thick mandibular corpus and unusually large postcanine tooth crowns with thick enamel. Leakey 1959 describes OH 5, the type specimen of P. boisei, and Tobias 1967, a classic monograph, reviews its unusual morphology and compares it to the hominins known at the time. Brown, et al. 1993 confirms that P. boisei shows high levels of cranial, but not canine, sexual dimorphism, and Wood, et al. 1994 presents evidence that the taxon shows little evidence of change across many hundreds of thousands of years. Arambourg and Coppens 1968 describes the type specimen of what we now call P. aethiopicus, and Walker, et al. 1986 describes what is very likely a cranium of the same taxon. Constantino and Wood 2007 reviews the paleobiology of P. boisei.

                                                                                                                                • Arambourg, C., and Y. Coppens. 1968. Découverte d’un Australopithecien nouveau dans les gisements de L’Omo (Ethiopie). South African Journal of Science 64.2: 58–59.

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                                                                                                                                  The announcement of the holotype of what was to become Paranthropus aethiopicus.

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                                                                                                                                  • Brown, B., A. Walker, C. V. Ward, and R. E. F. Leakey. 1993. New Australopithecus boisei calvaria from East Lake Turkana, Kenya. American Journal of Physical Anthropology 91.2: 137–159.

                                                                                                                                    DOI: 10.1002/ajpa.1330910202Save Citation »Export Citation »E-mail Citation »

                                                                                                                                    These fossils confirm that Paranthropus boisei shows substantial sexual dimorphism in the size and the shape of the cranium. Available online for purchase or by subscription.

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                                                                                                                                    • Constantino, P., and B. Wood. 2007. The evolution of Zinjanthropus boisei. Evolutionary Anthropology: Issues, News, and Reviews 16.2: 49–62.

                                                                                                                                      DOI: 10.1002/evan.20130Save Citation »Export Citation »E-mail Citation »

                                                                                                                                      How discoveries changed the way researchers interpret this distinctive archaic hominin taxon. Available online for purchase or by subscription.

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                                                                                                                                      • Leakey, L. S. B. 1959. A new fossil skull from Olduvai. Nature 184.4685: 491–493.

                                                                                                                                        DOI: 10.1038/184491a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                        Louis Leakey makes the case that the OH 5 cranium sampled a hitherto unknown archaic hominin, Zinjanthropus boisei, in East Africa. It is now referred to as Paranthropus boisei.

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                                                                                                                                        • Tobias, P. V. 1967. The cranium and maxillary dentition of Australopithecus (Zinjanthropus) boisei. Vol. 2. Edited by L. S. B. Leakey. Olduvai Gorge. Cambridge, UK: Cambridge Univ. Press.

                                                                                                                                          DOI: 10.1017/CBO9780511897795Save Citation »Export Citation »E-mail Citation »

                                                                                                                                          One of the classic publications of paleoanthropology, this monograph focuses on the detailed morphology and relationships of the OH 5 cranium, the holotype of Paranthropus boisei.

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                                                                                                                                          • Walker, A., R. E. Leakey, J. M. Harris, and F. H. Brown. 1986. 2.5-Myr Australopithecus boisei from west of Lake Turkana, Kenya. Nature 322.6079: 517–522.

                                                                                                                                            DOI: 10.1038/322517a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                            The announcement of a cranium that has been interpreted either as an early variant of Paranthropus boisei or as the type of cranium that may well match the mandible that is the holotype of Paranthropus aethiopicus. Available online by subscription.

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                                                                                                                                            • Wood, B. A., C. W. Wood, and L. W. Konigsberg. 1994. Paranthropus boisei: An example of evolutionary stasis? American Journal of Physical Anthropology 95.2: 117–136.

                                                                                                                                              DOI: 10.1002/ajpa.1330950202Save Citation »Export Citation »E-mail Citation »

                                                                                                                                              These authors claim there has been little consistent directional change in the morphology of Paranthropus boisei over a period of close to a million years. Available online for purchase or by subscription.

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                                                                                                                                              Archaic Hominins from Southern Africa

                                                                                                                                              The first archaic hominin to be discovered in Africa was recovered in 1924 from the Taungs (also known as Taung) Limeworks, seventy-five miles north of Kimberley, in what is now South Africa. In the following year, in a letter to the journal Nature, Raymond Dart attributed the child’s skull from Taung to a new species and genus, Australopithecus africanus. Comparable finds at Sterkfontein and at Makapansgat were initially attributed to different genera and species, but they were later included within Au. africanus, as were hominins recovered more recently from Gladysvale Cave, which is close to Sterkfontein. Fossils with slightly larger postcanine teeth (i.e., premolars and molars), more robust jaws, and flatter faces were found at Kromdraai and Swartkrans, and more recently at Drimolen, Gondolin, and Coopers. Like Sterkfontein, these are all cave sites in and around the Blaauwbank Valley near Krugersdorp, approximately equidistant from Pretoria and Johannesburg. These larger-toothed (also known as megadont) fossils were assigned to a second genus, Paranthropus, as Paranthropus robustus. Robinson 1954 is a classic paper that reviews the differences between Australopithecus and Paranthropus.

                                                                                                                                              • Robinson, J. T. 1954. The genera and species of the Australopithecinae. American Journal of Physical Anthropology 12.2: 181–200.

                                                                                                                                                DOI: 10.1002/ajpa.1330120216Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                A seminal paper in which John Robinson surveys the fossil hominin evidence from southern Africa and rationalizes its taxonomy and phylogenetic relationships. Available online for purchase or by subscription.

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                                                                                                                                                Australopithecus from Southern Africa

                                                                                                                                                Dart 1925 attributes the child’s skull from Taung to a new species and genus, Australopithecus africanus. Comparable finds at Sterkfontein and at Makapansgat were initially attributed to different genera and species (Broom 1936, Dart 1948), but they were later included within Au. africanus, as were hominins recovered more recently from Gladysvale Cave, near Sterkfontein. Some researchers believe that fossil hominin remains from a relatively unexplored lower part of the Sterkfontein cave complex (Member 2 and the Jacovec Cavern) push the southern African fossil record back to 4 Ma, and perhaps beyond (Clarke 1998). But this old date has been challenged and is probably wrong, and recent attempts to date sediments at Sterkfontein have come up with dates that are consistently younger (Pickering, et al. 2019). Two associated skeletons found at a site called Malapa have been assigned to a separate species, Australopithecus sediba (Berger, et al. 2010; Pickering, et al. 2011; Berger 2013). It has been claimed the Jacovec and Member 2 fossils sample a more primitive hominin species than Au. africanus, and the Malapa fossils sample a taxon that is intermediate between Au. africanus and Homo, but both could also be variants of Au. africanus (Kimbel 2013).

                                                                                                                                                • Berger, L. R. 2013. The mosaic nature of Australopithecus sediba. Science 340.6129: 163–165.

                                                                                                                                                  DOI: 10.1126/science.340.6129.163Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                  This is the introduction to two reports and four research articles that present interpretations of the dentition, mandibles, upper limb, axial skeleton, and lower limb of Australopithecus sediba. The introduction and the papers stress that knowledge of existing hominins would not have allowed researchers to predict the combinations of morphology the researchers claim are seen in Au. sediba. Available online by subscription.

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                                                                                                                                                  • Berger, L. R., D. J. de Ruiter, S. E. Churchill, et al. 2010. Australopithecus sediba: A new species of Homo-like australopith from South Africa. Science 328.5975: 195–204.

                                                                                                                                                    DOI: 10.1126/science.1184944Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                    Berger and colleagues claim that Australopithecus sediba is distinct from Australopithecus africanus, and that it is the immediate ancestor of Homo. Not everyone agrees with them (see Kimbel 2013). Available online by subscription.

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                                                                                                                                                    • Broom, R. 1936. New fossil anthropoid skull from South Africa. Nature 138.3490: 486–488.

                                                                                                                                                      DOI: 10.1038/138486a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                      Broom’s assessment of a fragmentary cranium found at Sterkfontein (TM 1511) was that it “probably agrees fairly closely with the Taungs ape” (p. 488), but nonetheless he placed it in a new Australopithecus species, Australopithecus transvaalensis.

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                                                                                                                                                      • Clarke, R. J. 1998. First ever discovery of a well-preserved skull and associated skeleton of Australopithecus. South African Journal of Science 94.10: 460–463.

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                                                                                                                                                        A remarkably complete hominin-associated skeleton, StW 573, was discovered deep in the Sterkfontein cave in Member 2. Magnetostratigraphy and cosmogenic nuclide dating evidence were interpreted as suggesting an age between 4 and 3 Ma, but more-recent results from uranium-lead dating applied to speleothems (i.e., flowstones, stalactites, and stalagmites) close to the skeleton suggest that the Member 2 breccia is less than 3 Ma.

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                                                                                                                                                        • Dart, R. A. 1925. Australopithecus africanus: The man-ape of South Africa. Nature 115.2884: 195–199.

                                                                                                                                                          DOI: 10.1038/115195a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                          Dart’s prescient justification for erecting a new genus to accommodate a juvenile hominin that was obviously different from anything that had been recovered and reported hitherto.

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                                                                                                                                                          • Dart, R. A. 1948. The Makapansgat proto-human Australopithecus prometheus. American Journal of Physical Anthropology 6.3: 259–284.

                                                                                                                                                            DOI: 10.1002/ajpa.1330060304Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                            The first fossil hominins from Makapansgat were reported by Raymond Dart, who allocated them to yet another new species of Australopithecus, Australopithecus prometheus. Dart chose this name because he considered the Makapansgat hominins were capable of making fire. Available online for purchase or by subscription.

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                                                                                                                                                            • Kimbel, W. H. 2013. Hesitation on hominin history. Nature 497.7451: 573–574.

                                                                                                                                                              DOI: 10.1038/497573aSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                              Kimbel sets out the case that Australopithecus sediba is more parsimoniously interpreted as a variant of Australopithecus africanus.

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                                                                                                                                                              • Pickering, R., P. H. G. M. Dirks, Z. Jinnah, et al. 2011. Australopithecus sediba at 1.977 Ma and implications for the origins of the genus Homo. Science 333.6048: 1421–1423.

                                                                                                                                                                DOI: 10.1126/science.1203697Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                Pickering and colleagues exploit uranium-lead dating to generate a remarkably precise date for the Malapa hominins. Available online by subscription.

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                                                                                                                                                                • Pickering, R., A. I. R. Herries, J. D. Woodhead, et al. 2019. U-Pb-dated flowstones restrict South African early hominin record to dry climate phases. Nature 565:226–230.

                                                                                                                                                                  DOI: 10.1038/s41586-018-0711-0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                  Pickering and colleagues applied uranium-lead dating to flowstones included in the caves and not only generated ages for the flowstones, but also found that because the flowstones formed simultaneously during periods of higher rainfall they can be used to put the caves in relative date order (also known as seriation). Available online by subscription.

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                                                                                                                                                                  Paranthropus from Southern Africa

                                                                                                                                                                  Fossils with slightly larger postcanine (i.e., premolars and molars) tooth crowns, more robust jaws, and flatter faces than those of Australopithecus africanus were found at Kromdraai B (Broom 1938; Thackeray, et al. 2001; Braga, et al. 2017), Swartkrans (Broom 1949), Drimolen (Keyser 2000; Keyser, et al. 2000), Gondolin, and Coopers, all of which are cave sites in and around the Blaauwbank Valley. This more megadont material was assigned to a second genus, Paranthropus, as Paranthropus robustus, and along with the remains of hyper-megadont hominins from East Africa that are reviewed under Hyper-megadont Archaic Hominins from East Africa, they are referred to as the “robust” australopiths because of their large faces, jaws, and postcanine tooth crowns. Wood and Schroer 2013 discusses the relationships between P. robustus and Paranthropus boisei.

                                                                                                                                                                  Transitional Hominins

                                                                                                                                                                  A series of discoveries in the early 1960s at Olduvai Gorge prompted Louis Leakey, Phillip Tobias, and John Napier to propose in 1964 that the remains represented a new, more primitive species of the genus Homo. Leakey, et al. 1964 named it Homo habilis (literally “handy man”). Critics considered the new taxon to be unjustified, with some claiming the new material was indistinguishable from Australopithecus africanus, and others regarding it as being more closely related to Homo erectus (see Homo habilis). Discoveries made at Koobi Fora in Kenya were added to the fossil evidence for early Homo, and this prompted some researchers to claim that the extent and nature of the variation in early Homo was excessive for a single species, so it was proposed that the material in early Homo should be allocated to two species. One widely adopted scheme (Wood 1992, Schrenk 2013) recognizes Homo habilis sensu stricto, with OH 7 as its type specimen, as one of the two species. This taxon is best known from Olduvai Gorge and the Omo-Turkana region. The other, Homo rudolfensis, of which KNM-ER 1470 is the type specimen (Alexeev 1986), is, as yet, known only in East Africa from sites in the Omo-Turkana Basin. Tobias and Koenigswald 1964 finds no evidence of transitional hominins in Southeast Asia. Some researchers have gone full circle and have questioned whether it is appropriate to include these fossils in Homo (Wood and Collard 1999).

                                                                                                                                                                  Homo habilis

                                                                                                                                                                  Fossil evidence for Homo habilis comes from several sites in East Africa (Kimbel, et al. 1997) and perhaps also from southern Africa (Hughes and Tobias 1977). Evidence from Olduvai made it clear that H. habilis was a good taxon, and not a mix of Australopithecus africanus and Homo erectus (Leakey, et al. 1971). In some ways H. habilis is not like later Homo (Johanson, et al. 1987; Tocheri, et al. 2007; Ruff 2009), and some have suggested (see Transitional Hominins) that it no longer makes sense to include H. habilis within Homo.

                                                                                                                                                                  • Hughes, A. R., and P. V. Tobias. 1977. A fossil skull probably of the genus Homo from Sterkfontein, Transvaal. Nature 265.5592: 310–312.

                                                                                                                                                                    DOI: 10.1038/265310a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                    The first evidence of a Homo habilis–like cranium from southern Africa. Available online by subscription.

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                                                                                                                                                                    • Johanson, D. C., F. T. Masao, G. G. Eck, et al. 1987. New partial skeleton of Homo habilis from Olduvai Gorge, Tanzania. Nature 327.6119: 205–209.

                                                                                                                                                                      DOI: 10.1038/327205a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                      The paper announced the recovery of OH 62, one of the few reliable sources of evidence about the postcranial skeleton of Homo habilis. Available online by subscription.

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                                                                                                                                                                      • Kimbel, W. H., D. C. Johanson, and Y. Rak. 1997. Systematic assessment of a maxilla of Homo from Hadar, Ethiopia. American Journal of Physical Anthropology 103.2: 235–262.

                                                                                                                                                                        DOI: 10.1002/(SICI)1096-8644(199706)103:2%3C235::AID-AJPA8%3E3.0.CO;2-SSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                        This hominin maxilla is among the earliest evidence for Homo. Available online for purchase or by subscription.

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                                                                                                                                                                        • Leakey, M. D., R. J. Clarke, and L. S. B. Leakey. 1971. New hominid skull from Bed I, Olduvai Gorge, Tanzania. Nature 232.5309: 308–312.

                                                                                                                                                                          DOI: 10.1038/232308a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                          The discovery of OH 24 meant that one of the earliest of the Homo habilis crania from Olduvai Gorge was also one of the most Homo erectus–like, thus blunting the criticism that H. habilis was a mix of earlier fossils belonging to an archaic hominin and later fossils belonging to H. erectus. Available online by subscription.

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                                                                                                                                                                          • Ruff, C. 2009. Relative limb strength and locomotion in Homo habilis. American Journal of Physical Anthropology 138.1: 90–100.

                                                                                                                                                                            DOI: 10.1002/ajpa.20907Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                            The strength of the humerus (upper arm) and the femur (thigh) in apes is similar, whereas in modern humans the latter is stronger than the former. The OH 62 Homo habilis skeleton shows the ape pattern. Available online for purchase or by subscription.

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                                                                                                                                                                            • Tocheri, M. W., C. M. Orr, S. G. Larson, et al. 2007. The primitive wrist of Homo floresiensis and its implications for hominin evolution. Science 317.5845: 1743–1745.

                                                                                                                                                                              DOI: 10.1126/science.1147143Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                              The wrist bones of Homo habilis share many features with those of Australopithecus afarensis. Available online by subscription.

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                                                                                                                                                                              Homo rudolfensis

                                                                                                                                                                              Wood 1992 presents a scheme for early Homo that recognizes a second taxon, Homo rudolfensis, with KNM-ER 1470 as the type specimen, in addition to Homo habilis sensu stricto. It is not clear whether any postcranial remains can be confidently assigned to H. rudolfensis (Wood and Collard 1999, cited under Transitional Hominins). A mandible from Koobi Fora, KNM-ER 1802, had been assigned to H. rudolfensis, but Leakey, et al. 2012 suggests that more recent discoveries cast doubt on this assignment.

                                                                                                                                                                              • Leakey, M. G., F. Spoor, M. C. Dean, et al. 2012. New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo. Nature 488.7410: 201–204.

                                                                                                                                                                                DOI: 10.1038/nature11322Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                A small, well-preserved face (KNM-ER 62000) looks to be a good candidate for a smaller-bodied (presumed female) member of the same taxon as KNM-ER 1470. A well-preserved lower jaw (KNM-ER 60000) and a fragmentary lower jaw (KNM-ER 62003) seem to be better matches for the type of facial morphology seen in KNM-ER 1470 and KNM-ER 62000 than the type of mandible (e.g., KNM-ER 1802) that had been suggested as belonging to Homo rudolfensis. Available online by subscription.

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                                                                                                                                                                                • Wood, B. A. 1992. Origin and evolution of the genus Homo. Nature 355.6363: 783–790.

                                                                                                                                                                                  DOI: 10.1038/355783a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                  The paper suggests fossils that might belong to a second early Homo taxon. Available online by subscription.

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                                                                                                                                                                                  Premodern Homo

                                                                                                                                                                                  Premodern Homo comprises all the extinct taxa included in Homo other than the two Homo taxa subsumed in the transitional hominin grade (see Transitional Hominins). The criteria for inclusion in the premodern Homo grade is morphology that is distinct from australopiths and transitional hominins (e.g., less robust mandibular bodies and smaller postcanine tooth crowns) and/or morphology that lies outside the range we associate with anatomically modern humans (i.e., Homo sapiens).

                                                                                                                                                                                  Homo erectus

                                                                                                                                                                                  These publications relate to the classic Indonesian and Chinese evidence for Homo erectus. There is evidence that H. erectus (Dubois 1893, Black 1927) persisted in Asia for well over a million years (c. 1.8 to c. 0.2 Ma), so H. erectus in Asia overlapped temporally with Homo sapiens in Africa (Swisher, et al. 1994; Swisher, et al. 1996).

                                                                                                                                                                                  • Black, D. 1927. On a lower molar hominid tooth from Chou-Kou-Tien deposit. Palaeontologia Sinica, ser. D 7.1: 1–28.

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                                                                                                                                                                                    Davidson Black establishes a new genus and species, Sinanthropus pekinensis, for a tooth recovered from the Lower Cave at what is now called Zhoukoudian.

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                                                                                                                                                                                    • Dubois, E. 1893. Pithecanthropus erectus: Eine menschenaehnliche Übergangsform aus Java. Batavia: Landesdruckerei.

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                                                                                                                                                                                      Eugène Dubois’s initial assessment was that the Trinil fossils belonged to an upright ape (hence, their initial binomial, Anthropopithecus erectus), but in this paper he suggests they are primitive ancestors of modern humans, so he moves the species to a newly established genus, Pithecanthropus.

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                                                                                                                                                                                      • Swisher, C. C., III, G. H. Curtis, T. Jacob, A. G. Getty, A. Suprijo, and Widiasmoro. 1994. Age of the earliest known hominids in Java, Indonesia. Science 263.5150: 1118–1121.

                                                                                                                                                                                        DOI: 10.1126/science.8108729Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                        Argon-argon dating suggests that most of the Javan hominins are older—between c. 1.9 and 1.6 Ma—than previously appreciated. Available online by subscription.

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                                                                                                                                                                                        • Swisher, C. C., III, W. J. Rink, S. C. Antón, et al. 1996. Latest Homo erectus of Java: Potential contemporaneity with Homo sapiens in Southeast Asia. Science 274.5294: 1870–1874.

                                                                                                                                                                                          DOI: 10.1126/science.274.5294.1870Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                          Evidence of a young age—perhaps between forty and twenty thousand years old (ka)—for the Ngandong hominins, but most researchers consider the evidence is more consistent with these remains being closer to 200 ka. Available online by subscription.

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                                                                                                                                                                                          Homo ergaster

                                                                                                                                                                                          The publications in this subsection relate to Homo erectus–like fossils from sites in Africa and western Eurasia that may belong to a separate taxon, Homo ergaster. By perhaps 2.0 Ma, and certainly by c. 1.7 Ma, the remains of H. ergaster (Groves and Mazák 1975; Brown, et al. 1985) (also known as early African Homo erectus), appear in sites in the Omo-Turkana region of East Africa. What distinguishes H. ergaster from all the hominin taxa that have been referred to thus far is a reduction in the relative and absolute size of the face, jaws, and chewing teeth, perhaps a reduction in sexual dimorphism (Villmoare, et al. 2019) although the discovery of small-brained H. erectus (Spoor, et al. 2007) challenged this hypothesis, plus a postcranial skeleton whose morphology is consistent with H. ergaster being an obligate biped. The earliest hominin fossil evidence outside Africa is c. 1.8 Ma. Fossils of this age, or close to it, are known from Dmanisi, Georgia (Gabunia and Vekua 1995; Rightmire, et al. 2006; Lordkipanidze, et al. 2007). The crania from Dmanisi in some ways resemble H. ergaster and, in other ways, Homo habilis. Other than these sites and an archaeological site in the Near East called Ubeidiya, the evidence for hominin occupation in Europe much before 1 Ma is weakened either by unreliable dating or by the inconclusive nature of the paleontological or archaeological evidence; a c. 1.2 Ma mandible from deposits in the Sima del Elefante at Atapuerca is an exception (Carbonell, et al. 2008). Were the first hominins to leave Africa H. ergaster–like, or were they more primitive H. habilis–like hominins?

                                                                                                                                                                                          Homo heidelbergensis

                                                                                                                                                                                          The distinctive morphology of Homo erectus gives way to hominins with a less specialized, but still quite robust, skull and postcranial skeleton (i.e., relatively wide mandibular body and well-developed ectocranial features in the skull, and thick cortex and relatively thick long-bone shafts in the postcranial skeleton). There is an ongoing debate about the degree of regional distinctiveness of these remains, which include fossil crania from sites such as Kabwe in Africa (Woodward 1921), Petralona and Mauer (Schoetensack 1908) in Europe, and Jinnuishan in China. There is no consensus about the most appropriate taxonomy for this material. Some researchers support species-level distinctions (e.g., Homo rhodesiensis, Homo antecessor [Bermúdez de Castro, et al. 1997]), while others are content to recognize the variability as no more than an expression of polytypic, intraspecific variation within an inclusive interpretation of Homo sapiens that would see that taxon subsume all of Homo more recent than H. erectus. Mounier, et al. 2009; Stringer 2012; and Hublin 2013 provide helpful reviews of a particularly contentious part of the hominin fossil record.

                                                                                                                                                                                          Homo neanderthalensis

                                                                                                                                                                                          The species Homo neanderthalensis (King 1864; Schmitz, et al. 2002) is a subset of premodern Homo that has what many, but not all, researchers interpret as a sufficiently distinctive morphology that it deserves to be recognized as a separate species. Neanderthals are found at sites spread across Europe, the Near East, and western Asia that range in age from greater than c. 200 ka (this date would be earlier if the Sima de los Huesos material [Arsuaga, et al. 1997] is included) to c. 30 ka. Their distinctive facial shape, robust long bones, and large joints have been interpreted as being a phenotypic consequence of their occupying cold and marginal environments, equipped only with relatively unrefined tools. Harvati-Papatheodorou 2013 reviews the fossil evidence for Neanderthals. The evidence from the Sima de los Huesos suggests that the distinctive features of Neanderthals did not appear simultaneously, with dental features appearing earlier and changes in the shape of the brain appearing later (Poza-Rey, et al. 2019).

                                                                                                                                                                                          Molecular Evidence for Homo neanderthalensis

                                                                                                                                                                                          The molecular studies of Krings, et al. 1997; Green, et al. 2008; and Green, et al. 2010 have provided important evidence about whether Neanderthals are a separate species, and thus about the relationship between Neanderthals and modern humans.

                                                                                                                                                                                          Homo naledi

                                                                                                                                                                                          This taxon comprises hominin remains recovered from two chambers, Dinaledi (Berger, et al. 2015) and Lesedi (Hawks, et al. 2017), in the Rising Star cave system near the site of Swartkrans, in Gauteng Province, South Africa. The fossils belonging to H. naledi display relatively little among-individual variation, and sample a hominin with an unusual mix of characteristics. Cranially it resembles early Homo/H. ergaster, but with a smaller endocranial volume (c. >550 cm3), dentally it combines derived (i.e., modern human-like) tooth crowns with primitive mandibular premolar roots, and postcranially the hand morphology is mostly derived in the direction of modern humans (Kivell, et al. 2015), yet the pedal phalanges are curved (Harcourt-Smith, et al. 2015) and the morphology of the pelvis and hip joint is relatively primitive. All of the hominin fossils in the Dinaledi Chamber were recovered from the same horizon, subunit 3b (Dirks, et al. 2015). The sediments and fossils in that subunit were subsequently dated using several techniques and the results suggested that the most likely age of H. naledi from the Dinaledi Chamber is the maximum age from US-ESR, which is 253 +82/−70 ka (Dirks, et al. 2017). The hominins from the Lesedi Chamber are undated.

                                                                                                                                                                                          Denisovans

                                                                                                                                                                                          Mitochondrial DNA recovered from a finger bone (Krause, et al. 2010) and from teeth (Reich, et al. 2010; Meyer, et al. 2015) recovered from Denisova Cave is different enough from that of Neanderthals that it is considered to belong to a distinct population presently called the Denisovans (Reich, et al. 2011). In addition to the finger bone, the only other fossil evidence from Denisova Cave consists of isolated tooth crowns and bone fragments, one of which may be the result of mating between a Neanderthal mother and a Denisovan father (Slon, et al. 2018). Ancient proteins recovered from a mandible found in a cave in Tibet matches comparable evidence from one of the Denisovan teeth (D3) (Chen, et al. 2019), so the Xiahe mandible may be the best fossil evidence we have of the Denisovans. It has been suggested there may be as many as three Denisovan lineages (Jacobs, et al. 2019).

                                                                                                                                                                                          Homo floresiensis

                                                                                                                                                                                          Fossil evidence from Flores, an island in Indonesia, of a relatively recent fossil hominin is best interpreted as a dwarfed version of premodern Homo–grade hominin such as Homo erectus, although some of its morphology is closer to that of the transitional hominins. Brown, et al. 2004 announces the initial Homo floresiensis fossil finds; Morwood and Jungers 2009 provides an authoritative assessment of their implications for hominin evolution. Sutikna, et al. 2016 reports the most recent age estimates for Liang Bua, and van den Bergh, et al. 2016 suggests that the discovery of a mandible on Flores could extend the temporal range of H. floresiensis back to c. 700 ka.

                                                                                                                                                                                          • Brown, P., T. Sutikna, M. J. Morwood, et al. 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431.7012: 1055–1061.

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                                                                                                                                                                                            Announcement of the discovery of the LB 1, the associated skeleton of a diminutive, small-brained individual whose morphology is emphatically not that of a modern human.

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                                                                                                                                                                                            • Morwood, M. J., and W. L. Jungers. 2009. Conclusions: Implications of the Liang Bua excavations for hominin evolution and biogeography. In Special issue: Paleoanthropological research at Liang Bua, Flores, Indonesia. Edited by M. J. Morwood and W. L. Jungers. Journal of Human Evolution 57.5: 640–648.

                                                                                                                                                                                              DOI: 10.1016/j.jhevol.2009.08.003Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                              Summary of the fossil evidence for Homo floresiensis. Available online by subscription.

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                                                                                                                                                                                              • Sutikna, T., M. W. Tocheri, M. J. Morwood, et al. 2016. Revised stratigraphy and chronology for Homo floresiensis at Liang Bua in Indonesia. Nature 532:366–369.

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                                                                                                                                                                                                A fresh assessment of the stratigraphy in the Liang Bua cave, plus new luminescence dates, suggest that the fossils belonging to Homo floresiensis date from 100 ka to 60 ka, and the artifacts from 190 ka to 60 ka. Available online by subscription.

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                                                                                                                                                                                                • van den Bergh, G. D., Y. Kaifu, I. Kurniawan, et al. 2016. Homo floresiensis-like fossils from the early Middle Pleistocene of Flores. Nature 534:245–248.

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                                                                                                                                                                                                  Report of the discovery of a H. floresiensis–like mandible in Mata Menge, another cave on Flores, which would, if it proves to belong to H. floresiensis, extend the temporal range of that taxon back to c. 700 ka. Available online by subscription.

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                                                                                                                                                                                                  Homo luzonensis

                                                                                                                                                                                                  Hominin fossils recovered from Callao Cave on northern Luzon in the Philippines have been assigned to a novel species, Homo luzonensis (Détroit, et al. 2019). Stone tools from northern Luzon may push the date of H. luzonensis back to c. 700ka (Ingicco, et al. 2018).

                                                                                                                                                                                                  • Détroit, F., A. S. Mijares, J. Corny, et al. 2019. A new species of Homo from the Late Pleistocene of the Philippines. Nature 568:181–186.

                                                                                                                                                                                                    DOI: 10.1038/s41586-019-1067-9Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                    Researchers make the case that this modest collection of hominin fossils samples a taxon with a unique mix of primitive (hand and foot bones) and derived (dental) features, and they propose it deserves recognition as a novel species, Homo luzonensis. Available online by subscription.

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                                                                                                                                                                                                    • Ingicco, T., G. D. van den Bergh, C. Jago-on, et al. 2018. Earliest known hominin activity in the Philippines by 709 thousand years ago. Nature 557:233–237.

                                                                                                                                                                                                      DOI: 10.1038/s41586-018-0072-8Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                      Researchers report the recovery of stone tools from Kalinga in the Cagayan Valley, also on northern Luzon and, if they were fashioned by the Callao hominins, this would push the date of Homo luzonensis back to between 777 and 631 ka. Available online by subscription.

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                                                                                                                                                                                                      Anatomically Modern Humans

                                                                                                                                                                                                      The origin of modern humans is a topic that has dominated human evolutionary studies since at least the turn of the 21st century. The crux of the debate is whether or not anatomically modern humans originated from one or more migrations out of Africa, or whether they originated effectively independently in different regions of the world. In the out-of-Africa hypothesis, successive migrations each took their gene pools with them, so that anatomically modern humans everywhere have a genome that is made up mainly of genes that originated in Africa. The competing hypothesis is that modern humans arose by a series of regional transitions from archaic to anatomically modern humans with, or without, significant admixture with later immigrants from Africa. The latter hypothesis allows for genes to be transferred between regions (either by migration of interbreeding), but it also implies there was substantial morphological continuity within each major region through time. Under the out-of-Africa hypothesis, the conventional wisdom was that the modern humans in each of the major regions of the world are descended from founder populations, each of which is derived from the most recent wave of modern human migrants from Africa. Thus, when that wave reached a major region of the world, it provided the ancestors of the modern humans living in that region today. This scenario suggests that regions closer to Africa would have experienced longer periods of local continuity than regions further from Africa. Reich 2018 suggests that the reality is more complex. When the researchers analyzed ancient DNA sequences recovered from anatomically modern human fossils ten(s) of thousands of years old, they found many instances where the sequences from subrecent modern human fossils from a region are more than subtly different from the sequences of the modern humans living in that region today. Reich and his colleagues suggest that the peopling of Europe involved hypothetical ancient “ghost” populations for which for the most part we only have the equivalent of circumstantial evidence. Until recently, the earliest fossil evidence of a hominin with a morphology that is closer to modern humans than to that of any extinct hominin was Omo I, one of the two crania from Kibish in Ethiopia (Day and Stringer 1991), which researchers have suggested are c. 190 ka (McDougall, et al. 2005), and the c. 170 ka modern human–like crania from Herto in the Middle Awash, Ethiopia (White, et al. 2003). Most recently, Hublin, et al. 2017 suggests that additional evidence from Jebel Irhoud strengthens the claim that hominins from that site “sample early stages of the H. sapiens clade.” If there is a need for a taxon for fossils known informally as archaic modern humans, Dreyer 1935 made the taxon Homo helmei available. Stringer 2002 and Collard and Dembo 2013 provide helpful reviews.

                                                                                                                                                                                                      • Collard, M., and M. Dembo. 2013. Modern human origins. In A companion to paleoanthropology. Edited by D. R. Begun, 557–581. Blackwell Companions to Anthropology 22. Oxford: Wiley-Blackwell.

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                                                                                                                                                                                                        An unbiased review of the origins of anatomically modern humans.

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                                                                                                                                                                                                        • Day, M. H., and C. B. Stringer. 1991. Les restes crâniens d’Omo-Kibish et leur classification à l’intérieur du genre Homo. L’Anthropologie 95.2–3: 573–594.

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                                                                                                                                                                                                          A consideration of the anatomically modern human–like Omo I cranium and the less anatomically modern human–like Omo II cranium from Kibish in Ethiopia.

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                                                                                                                                                                                                          • Dreyer, T. 1935. A human skull from Florisbad, Orange Free State, with a note on the endocranial cast, by C. U. Ariens Kappers. Proceedings of the Academy of Science, Amsterdam 38:119–128.

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                                                                                                                                                                                                            If there is ever a need for a taxon for fossils known informally as archaic modern humans, the name Homo helmei would be available.

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                                                                                                                                                                                                            • Hublin, J. J., A. Ben-Ncer, S. E. Bailey, et al. 2017. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature 546:289–292.

                                                                                                                                                                                                              DOI: 10.1038/nature22336Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                              Researchers claim that a c. 300 ka cranium recovered from Jebel Irhoud may represent an early stage in the evolution of modern humans. Available online by subscription.

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                                                                                                                                                                                                              • McDougall, I., F. H. Brown, and J. G. Fleagle. 2005. Stratigraphic placement and age of modern humans from Kibish, Ethiopia. Nature 433.7027: 733–736.

                                                                                                                                                                                                                DOI: 10.1038/nature03258Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                The case for the Kibish hominins being c. 190 ka. Available online by subscription.

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                                                                                                                                                                                                                • Reich, D. 2018. Who we are and how we got here: Ancient DNA and the new science of the human past. New York: Pantheon.

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                                                                                                                                                                                                                  A clear presentation of the potential of ancient DNA for recovering the complexity of recent human evolutionary history.

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                                                                                                                                                                                                                  • Stringer, C. 2002. Modern human origins: Progress and prospect. Philosophical Transactions of the Royal Society of London B: Biological Sciences 357.1420: 563–579.

                                                                                                                                                                                                                    DOI: 10.1098/rstb.2001.1057Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                    A comprehensive review of the various hypotheses for the origin of modern humans. Available online by subscription.

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                                                                                                                                                                                                                    • White, T. D., B. Asfaw, D. deGusta, et al. 2003. Pleistocene Homo sapiens from Middle Awash, Ethiopia. Nature 423.6941: 742–747.

                                                                                                                                                                                                                      DOI: 10.1038/nature01669Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                      Announces the discovery of c. 170 ka anatomically modern human–like crania from Herto, Ethiopia. Available online by subscription.

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