Online research in philosophy

Debate about adaptationism in biology continues, in part because within “the” problem of assessing adaptationism, three distinct problems are mixed together. The three problems concern the assessment of three distinct adaptationist positions, each of which asserts the central importance of adaptation and natural selection to the study of evolution, but conceives this importance in a different way. As there are three kinds of adaptationism, there are three distinct "anti-adaptationist" positions as well. Or putting it more formally, there are three different dimensions here, and strongly adaptationist views, strongly anti-adaptationist views, and moderate views are possible for each dimension.

Elliott Sober (1987, 1993) and Orzack and Sober (forthcoming) argue that adaptationism is a very general hypothesis that can be tested by testing various particular hypotheses that invoke natural selection to explain the presence of traits in populations of organisms. In this paper, I challenge Sobers claim that adaptationism is an hypothesis and I argue that it is best viewed as a heuristic (or research strategy). Biologists would still have good reasons for employing this research strategy even if it turns out that natural selection is not the most important cause of evolution.

This contribution to the adaptationism debate elaborates the nature of constraints and their importance in evolutionary explanation and argues that the adaptationism debate should be limited to the issue of how to privilege causes in evolutionary explanation. I argue that adaptationist explanations are deeply conceptually dependent on developmental constraints, and explanations that appeal to constraints are dependant on the results of natural selection. I suggest these explanations should be integrated into the framework of historical causal explanation. Each strategy explicitly appeals to some aspect of the evolutionary process, while implicitly appealing to others. Thus, adaptationists and anti-adaptationists can offer complementary causal explanations of the same explanandum. This eliminates much of the adaptationism debate and explains why its adversaries regularly agree with each other more than they would like. The adaptationism issue that remains is a species of the general issue of how to privilege causes in explanation. I show how a proposed solution to this general problem might be brought to bear on evolutionary explanations, and investigate some difficulties that might arise due to the nature of the evolutionary process.

Evolutionary psychologists attempt to infer our evolved psychology from the selection pressures present in our ancestral environments. Their use of this inference strategy?often called ?adaptive thinking??is thought to be justified by way of appeal to a rather modest form of adaptationism, according to which the mind's adaptive complexity reveals it to be a product of selection. I argue, on the contrary, that the mind's being an adaptation is only a necessary and not a sufficient condition for the validity of adaptive thinking, and that evolutionary psychology's predictive project is in fact committed to an extremely strong and highly implausible form of adaptationism. According to this ?strong adaptationism,? the macroevolutionary trajectory of a population is determined by, and therefore predictable on the basis of, the selection pressures acting upon it. Not only is this form of adaptationism prima facie highly implausible, it requires making a number of naïve and likely false assumptions concerning the nature of heritable phenotypic variation in natural populations. In particular, it assumes that phenotypic variation is inevitably small in its extent, unbiased in its direction, and copious in its quantity. Because it is unlikely that these conditions obtain as a general rule, and even more unlikely that they obtained in early human populations, I conclude that there is little reason to believe that adaptive thinking can be used to infer the current structure of our minds from evidence of past selection pressures.

Two critiques of simple adaptationism are distinguished: anti-adaptationism and extended adaptationism. Adaptationists and anti-adaptationists share the presumption that an evolutionary explanation should identify the dominant simple cause of the evolutionary outcome to be explained. A consideration of extended-adaptationist models such as coevolution, niche construction and extended phenotypes reveals the inappropriateness of this presumption in explaining the evolution of certain important kinds of features—those that play particular roles in the regulation of organic processes, especially behavior. These biological or behavioral ‘levers’ are distinctively available for adaptation and exaptation by their possessors and for co-optation by other organisms. As a result they are likely to result from a distinctive and complex type of evolutionary process that conforms neither to simple adaptationist nor to anti-adaptationist styles of explanation. Many of the human features whose evolutionary explanation is most controversial belong to this category, including the female orgasm.

Godfrey-Smith ( 2001 ) has distinguished three types of adaptationism. This article builds on his analysis, and revises it in places, by distinguishing seven varieties of adaptationism. This taxonomy allows us to clarify what is at stake in debates over adaptationism, and it also helps to cement the importance of Gould and Lewontin’s ‘Spandrels’ essay. Some adaptationists have suggested that their essay does not offer any coherent alternative to the adaptationist programme: it consists only in an exhortation to test adaptationist hypotheses more thoroughly than was usual in the 1970s. Here it is argued that the ‘Spandrels’ paper points towards a genuinely non-adaptationist methodology implicit in much evolutionary developmental biology. This conclusion helps to expose the links between older debates over adaptationism and more recent questions about the property of evolvability.

This paper critically examines Jerry Fodor's latest attacks on evolutionary psychology. Contra Leda Cosmides and John Tooby, Fodor argues (i) there is no reason to think that human cognition is a Darwinian adaptation in the first place, and (ii) there is no valid inference from adaptationism about the mind to massive modularity. However, Fodor maintains (iii) that there is a valid inference in the converse direction, from modularity to adaptationism, but (iv) that the language module is an exception to the validity of this inference. I explore Fodor's arguments for each of these claims, and the interrelations between them. I argue that Fodor is incorrect on point (i), correct on point (ii), partially correct on point (iii), and incorrect on point (iv). Overall, his critique fails to show that adopting a broadly Darwinian approach to cognition is intellectually indefensible.

The fate of optimality modeling is typically linked to that of adaptationism: the two are thought to stand or fall together (Gould and Lewontin, Proc Relig Soc Lond 205:581–598, 1979; Orzack and Sober, Am Nat 143(3):361–380, 1994). I argue here that this is mistaken. The debate over adaptationism has tended to focus on one particular use of optimality models, which I refer to here as their strong use. The strong use of an optimality model involves the claim that selection is the only important influence on the evolutionary outcome in question and is thus linked to adaptationism. However, biologists seldom intend this strong use of optimality models. One common alternative that I term the weak use simply involves the claim that an optimality model accurately represents the role of selection in bringing about the outcome. This and other weaker uses of optimality models insulate the optimality approach from criticisms of adaptationism, and they account for the prominence of optimality modeling (broadly construed) in population biology. The centrality of these uses of optimality models ensures a continuing role for the optimality approach, regardless of the fate of adaptationism.

Strong adaptationists would explain complex organic designs as specific adaptations to particular ancestral environments. Weak adaptationists don't assume that complex organic functioning represents evolutionary design in the sense of niche-specific adaptation. For some domain-specific competencies (folkbiology) strong adaptationism is useful, not necessary. With group-level belief systems (religion), strong adaptationism can become spurious pseudo-adaptationism. In other cases (language), weak adaptationism proves productive.