Evolutionary Biology Evolutionary Trends
by
Douglas H. Erwin
  • LAST REVIEWED: 19 May 2017
  • LAST MODIFIED: 13 January 2014
  • DOI: 10.1093/obo/9780199941728-0007

Introduction

Evolutionary trends, whether macroevolutionary events across higher taxa and large spans of geologic time, or more circumscribed events within smaller clades, have long played a prominent role in evolutionary theory. The identification of trends in the history of life has been used as evidence for the increasing adaptedness of life, for evolutionary progress, and more recently as support for selection at multiple levels. Thus, trends are a key feature of many discussions of evolutionary patterns and process. For many decades the existence of a trend was often simply asserted by an author, sometimes accompanied by an interpretive sketch. More recently, however, standards for the elucidation of trends have become considerably more rigorous. Researchers are expected to distinguish active or driven trends from passive trends. An active or driven trend is one in which there is a shift in the mean value of some character because of selection or some other factor. Passive trends are those associated with an increase in “variance,” and from random fluctuations in trait values. Trends have been described in many different variables, most frequently in body size (Cope’s Rule), as well as in complexity; in rates of speciation, extinction, or diversification; and in a variety of ecological factors. Among some groups of anthropologists, trends in cultural patterns have also been described, although generally without the rigorous analysis now expected in biological systems.

General Overviews

The papers noted here provide general introductions to the study of trends, focusing on works discussing trends in the fossil record, as this is where the bulk of work on evolutionary trends has been published until recently. Jablonski 2010 and McShea 2001 provide general introductions. The Presidential Address in Gould 1988 lays out the difference between what have become known as passive and driven trends, and McNamara 1990, an edited book, contains a variety of papers examining trends, albeit largely qualitatively, in different clades. The review in McShea 1998 examines possible explanations for trends from a variety of different perspectives.

  • Gould, S. J. 1988. Trends as changes in variance: A new slant on progress and directionality in evolution. Journal of Paleontology 62:319–329.

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    Presidential addresses to scientific societies are often forgettable, but this paper sparked new research. Classic Gould, this address covers everything from baseball to foraminifera, leavened with the requisite Latin epigrams, but Gould distinguished between trends that involve changes in the mean and those that simply reflect increases in variance. Together with his overview of previous studies of fossil trends, these features make this a foundational paper. Available online for purchase or by subscription.

  • Jablonski, D. 2010. Macroevolutionary trends in time and space. In In search of the causes of evolution. Edited by P. R. Grant and B. R. Grant, 25–43. Princeton, NJ: Princeton Univ. Press.

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    An excellent introduction to recent issues in macroevolutionary trends in the fossil record, albeit from a non-phylogenetic perspective. Jablonski carefully distinguishes between different types of trends and discusses issues associated with trends in body size and in latitude, and their implications for macroevolution.

  • McNamara, K. J., ed. 1990. Evolutionary trends. Tucson: Univ. of Arizona Press.

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    Although now a bit dated and from a pre-phylogenetic era of work in paleontology, the contributors to this volume examine the dynamics of evolutionary trends in general, and in a host of invertebrate and vertebrate clades.

  • McShea, D. W. 1998. Possible largest-scale trends in organismal evolution: Eight “live hypotheses.” Annual Review of Ecology and Systematics 29:293–318.

    DOI: 10.1146/annurev.ecolsys.29.1.293E-mail Citation »

    In this review of the mechanisms underlying large-scale evolutionary trends, McShea evaluates eight hypotheses under active study: entropy, energy intensiveness, evolutionary versatility, developmental depth, structural depth, adaptedness, size, and complexity. This paper provides one of the broadest overviews of possible mechanisms for evolutionary trends. Available online for purchase or by subscription.

  • McShea, D. W. 2001. Evolutionary trends. In Palaeobiology II. Edited by D. E. G. Briggs and P. R. Crowther, 206–211. Oxford: Blackwell Science.

    DOI: 10.1002/9780470999295E-mail Citation »

    A general overview of evolutionary trends, highlighting the differences between passive and driven trends.

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