Some methodological adaptationists (perhaps unconsciously) hijacked the term “exaptation,” and took an occasion of Stephen Jay Gould’s misspeaking as confirmation that it possessed an evolutionarily “designed” function and was a version of an adaptation, something it was decidedly not. Others provided a standard of evidence for exaptation that was inappropriate, and based on an adaptationist worldview. This article is intended to serve as both an analysis of and correction to those situations. Gould and Elisabeth Vrba’s terms, “exaptation” and “aptation,” as originally introduced, are very useful, unlike the faded adaptationist echo of “exaptation” devised by the methodological adaptationists, which has made the term incoherent. We will discuss how exaptation relates to function, to aptation, and to adaptation, both primary and secondary. These ideas have been rendered practically useless through their mistaken definitions and misapplications by evolutionary psychologists.
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This article was first written with Stephen Jay Gould as my coauthor in the spring of 2002. All of the sections were drafted before he passed away in May 2002. It was our third cowritten paper. I left it alone for over ten years, until I finally realized that he would have liked our arguments to be published, so I updated and completed the manuscript on my own. I would like to acknowledge Steve’s contributions to this paper, both conceptual and structural.
Google Scholar lists 502 citations, accessed June 1, 2016.
Google Scholar lists 676 citations, accessed June 1, 2016.
Google Scholar lists 244 citations, accessed June 1, 2016.
Gould and Vrba then suggest: “The set of aptations existing at any one time consists of two partially overlapping subsets: the subset of adaptations and the subset of exaptations” (1982, p. 6). But this is not right; their definitions are clearly intended to divide aptations into non-overlapping categories of exaptation and adaptation, as is clear from both their diagram (1982, p. 5), and from the rest of their discussion.
Marta Linde-Medina (2011) claims that exaptation is completely non-explanatory, primarily because there is no single mechanism associated with the concept, emphasizing the role for “internalist” developmental and embryological biology to step in with the essential explanations for traits at this point (2011, p. 583). We find that exaptation can be explanatory in its contrasting role to secondary adaptations and adaptations (Gould and Vrba 1982, p. 11) as a form of aptation, even if a variety of mechanisms are involved in producing and maintaining the relevant originating traits, including exactly those she emphasizes.
See how their readers copied this mistake: e.g., “As discussed by Buss et al. (1998), many generally useful or ‘adaptive’ features of humans and other animals are not, strictly speaking, adaptations. Sometimes termed ‘exaptations’ (Gould and Vrba 1982), these useful functions arise as a consequence of other related features that are adaptations in the technical sense” (Schacter 1999, p. 197, emphasis added; Sherry and Schacter 1987). As defined by Gould and Vrba, exaptations do not have “functions,” they have effects.
I thank an anonymous reviewer for these comments.
For example, a trait cannot be an exaptation for x-ing if it was selected for x-ing, in which case it would be an adaptation for x-ing, but it could be an exaptation under a different description of the trait, e.g., for y-ing. For example, we can suppose that feathers were adapted for thermoregulation (as it is believed), but were at the same time exaptations for lift, or early flight, for some dinosaurs. Thank you to an anonymous reviewer for the question concerning this issue.
Gould says: ‘‘Elisabeth Lloyd, a philosopher of science at the University of California at San Diego, has just completed a critical study of explanations recently proposed by evolutionary biologists for the origins and significance of female orgasm. Nearly all these proposals follow the lamentable tradition of speculative storytelling in the a priori adaptationist mode’’ (1987a, p. 17).
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I would like to thank Ryan Ketcham for all of his help and support.
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Lloyd, E.A., Gould, S.J. Exaptation Revisited: Changes Imposed by Evolutionary Psychologists and Behavioral Biologists. Biol Theory 12, 50–65 (2017). https://doi.org/10.1007/s13752-016-0258-y
- Evolutionary by-product
- Evolutionary methodology
- Evolutionary psychology
- Female orgasm