In This Article Expand or collapse the "in this article" section Species Concepts

  • Introduction
  • General Overviews
  • Aristotle, Taxonomy, and Essentialism
  • The Origins of a Focus on Reproductive Barriers
  • Darwin’s Conception of Species
  • The Changing View of Species Leading Up to the Modern Synthesis
  • The Biological Species Concept
  • The Phylogenetic Species Concept
  • The BSC versus the PSC
  • The Evolutionary Species Concept
  • Niche-Based Conceptions of Species
  • The Challenge of Asexual Species
  • The Meaning of “Concept” in Species Concept Debates
  • Pluralism
  • Skepticism
  • Philosophy and the Human Component

Evolutionary Biology Species Concepts
Jody Hey
  • LAST REVIEWED: 13 December 2021
  • LAST MODIFIED: 30 July 2014
  • DOI: 10.1093/obo/9780199941728-0054


In a general and nontechnical sense, species are kinds of organisms. But for naturalists, from at least the early days of the age of the Enlightenment (late 1600s) up to the present day, there has been uncertainty and debate about just what species are and how best to identify them. Questions about species are central to some of the oldest and most-discussed philosophical topics on the nature of kinds of things (i.e., categories or universals). Perhaps surprisingly, the advent of the theory of evolution in the mid-19th century only accelerated debates and discussion about species and did little to resolve some of the basic disputes, even as scientists came to understand how new species arose. The 20th and 21st centuries have seen extraordinary growth in scientific research on species diversity, as well as increasing conservation efforts to avoid species extinction in the face of habitat loss and other anthropogenic forces of environmental change. All of the research on speciation, and species discovery, and on conservation takes place amid ongoing discussions about how best to identify species.

General Overviews

Because of a large philosophical element, the literature on species concepts is unusually diverse for a biological topic. A great many sources, including those from biologists, are concerned with topics such as the role of definitions, operational versus conceptual ideas, and the reality of taxonomic groups. Because of the diversity of opinions held by biologists on questions about species, the only broad reviews on the topic are edited volumes. Mayr 1957 is the first edited volume to attempt to address the species problem in some breadth, both philosophically and in application. Slobodchikoff 1976 and Ereshefsky 1992 are useful edited volumes that contain a number of the important philosophical papers on the subject (some papers are in both volumes). Otte and Endler 1989; Claridge, et al. 1997; and Howard and Berlocher 1998 are edited volumes of original articles, written mostly from biological perspectives rather than philosophical ones, on basic questions about species in general and on questions that arise in particular empirical contexts. Wilson 1999 is a volume of original philosophical articles, some of which have gone on to be widely cited, and Wilkins 2009 is a compendium of terms and concepts, useful for parsing the philosophical literature.

  • Claridge, M. F., H. A. Dawah, and M. R. Wilson, eds. 1997. Species: The units of biodiversity. Systematics Association Special Volume 54. London: Chapman & Hall.

    An edited volume with several very useful papers. The focus is largely on the practical aspects of species identification, rather than on philosophy or on the processes of speciation. Many articles address the practical issues that arise for species identification, in particular large taxonomic groups.

  • Ereshefsky, M., ed. 1992. The units of evolution: Essays on the nature of species. Cambridge, MA: MIT Press.

    An anthology of reprints of major, mostly philosophical, papers.

  • Howard, D. J., and S. H. Berlocher, eds. 1998. Endless forms: Species and speciation. New York: Oxford Univ. Press.

    A volume of original papers covering diverse topics related to species and speciation.

  • Mayr, E., ed. 1957. The species problem: A symposium presented at the Atlanta meeting of the American Association for the Advancement of Science, December 28–29, 1955. AAAS Publication 50. Washington, DC: American Association for the Advancement of Science.

    A volume of original papers, with the first and last by Ernst Mayr promoting the biological species concept.

  • Otte, D., and J. A. Endler, eds. 1989. Speciation and its consequences. Sunderland, MA: Sinauer.

    Although an edited volume with a broad scope, this book has a number of papers that became widely cited. The first section, with classic articles by Alan Templeton, Joel Cracraft, and Gareth Nelson, concerns species concepts directly, with the remainder of the book dwelling more on the speciation process.

  • Slobodchikoff, C. N., ed. 1976. Concepts of species. Benchmark Papers in Systematic and Evolutionary Biology 3. Stroudsburg, PA: Dowden, Hutchinson & Ross.

    An anthology of reprints of major papers, many of them philosophical in nature.

  • Wilkins, J. S. 2009. Defining species: A sourcebook from Antiquity to today. American University Studies V203. New York: Peter Lang.

    A terse encyclopedia covering the history of scientists and ideas relevant to questions about species.

  • Wilson, R. A., ed. 1999. Species: New interdisciplinary essays. Bradford Book. Cambridge, MA: MIT Press.

    A volume of original, mostly philosophical papers on the nature of species and the species problem.

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