Are Adapations Necessarily Genetic?
Steven J. Scher
Eastern Illinois University
Buss et al. (1998) are to be commended for clarifying concepts from evolutionary science, and detailing the utility of these concepts for psychology. Rather than contribute to the emotion-laden arguments that have accompanied much of the development of evolutionary psychology, Buss et al.'s contribution helps psychologists apply ideas from evolutionary biology to the study of mind and behavior.
However, Buss et al. err when they write that "there must be genes for an adaptation because such genes are required for the passage of the adaptation from parents to offspring" (p. 535). It is incorrect to say that genes are the only way behavioral or psychological features can be passed from parents to children. Decades of research has demonstrated that children are likely to have the same religion, political affiliation, and socioeconomic status as their parents. Surely, Buss et al. don't believe that there are genes for these characteristics. Nonetheless, these features have 'passed' from parents to offspring.
Buss et al. might argue that the examples given above are not adaptations because they don't solve an adaptive problem, or don't have the design features that characterize adaptations. However, there is nothing inherent in these features that precludes them from being adaptations, unless one simply defines an adaptation as being passed down by genes. There is no a priori reason why these features are any less likely to be adaptations than, for example, the tendency to be a short-term or long-term strategist in mating (Buss & Schmitt, 1993) or to solve problems of social deception (Cosmides, 1989).
Buss et al. define an adaptation as an "inherited and reliably developing characteristic that came into existence as a feature of a species through natural selection because it helped to directly or indirectly facilitate reproduction during the period of its evolution" (p. 535). However, the degree to which a feature facilitates reproduction -- its inclusive fitness -- "is not a property of an individual organism but rather a property of its actions or effects" (p. 534). It is the effects of a phenotype that determines whether those effects will be selected or not. How those phenotypic effects arise is irrelevant to the selection process.
Phenotypic psychological mechanisms surely arise through a complicated process. The role of genes is likely to be rather far away and indirect. Certainly, our current understanding of the relationship between mind and body limits our ability to understand how genes -- which code for physical structure -- contribute to psychological development. While the physical body can be measured in terms of the parameters of the physical world (e.g., mass, volume, velocity), these parameters do not apply to the mental world (Williams, 1985). Until parameters which apply in both domains can be identified, it will be difficult to understand how genes affect behavior.
In the meantime, it is entirely possible to imagine adaptations that 'reliably develop' not because specific genes have been developed for their assembly, but because a cultural transmission system has selected cultural products which facilitate reproduction. Take, for example, human mate selection. Buss (e.g., 1989) has convincingly demonstrated a set of sex differences that appear in many cultures. However, nothing in the data Buss has collected (nor, in the hypotheses he has generated) relate to a genetic basis for these differences. If the tendency of men to put a greater emphasis on physical attractiveness, for example, solved an adaptive problem for men, and if the emphasis on physical attractiveness by men could be acquired from one's parents through some form of social learning (a fact that seems not only possible, but likely), then males who acquired this tendency would have more children, and this tendency would therefore spread throughout society. (1)
Determining whether genetic or cultural selection (or, some combination) contributed to the evolution of a psychological adaptation requires a careful specification of a proposed natural history of the feature -- a point that Buss et al. appropriately make the focus of their article. This point is even more important given the position I advocate. The steps the feature has passed through, and the functions served at each of those stages should be described. The natural history should include a consideration of what means of transmission and what ontogenetic factors impact(ed) upon its development.
This natural history will generate evolutionary hypotheses. And, "all evolutionary hypotheses ... should be formulated in a precise enough manner to produce empirical predictions that can then be subjected to testing and potential falsification" (pp. 544-545). If one wants to comment on what means of selection led to the evolution of the adaptation, then these hypotheses should include predictions which would differ depending on whether there was genetic or cultural selection (Scher, 1997). If research confirms hypotheses which uniquely depend on there being 'genes for' a particular feature, then the genetic nature of the feature would be supported. If such differential hypotheses can not be generated, then one cannot address which method of selection was involved.
This does not mean that one cannot fruitfully continue to study the adaptation without determining which means of selection was involved. A theory will be valuable to the extent that it leads to more hypotheses and the collection of further data. Buss et al. cite a variety of studies that have been generated by adaptationist thinking, attesting to the strength of evolutionary psychology as a paradigm. However, few of these studies have anything to say about the genetics of the mechanisms studied, yet alone compare a genetic selection model to a cultural selection model.
Buss et al. make a valuable contribution to thinking on evolutionary psychology. However, their insistence that adaptations are by necessity genetic is in error. It is not valuable to omit viable mechanisms for the development of psychological features from study by definition. I encourage Buss et al -- and all psychological scientists -- to be even more "pluralistic about the conceptual tools of evolutionary psychology" (p. 545).
References
Buss, D.M. (1989). Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures. Behavioral and Brain Sciences, 12, 1-49.
Buss, D.M., Haselton, M.G., Shackelford, T.K., Bleske, A.L. & Wakefield, J.C. (1998). Adaptations, exaptations, and spandrels. American Psychologist, 53, 533-548.
Buss, D.M. & Schmitt, D.P. (1993). Sexual strategies theory: An evolutionary perspective on human mating. Psychological Review, 100, 204-232.
Cosmides, L. (1989). The logic of social exchange: Has natural selection shaped how humans reason? Studies with the Wason selection task. Cognition, 31, 187-276.
Scher, S.J. (1997). Five fallacies in thinking about evolution and human psychology. Unpublished manuscript, Eastern Illinois University.
Williams, G.C. (1985). A defense of reductionism in evolutionary biology. In R. Dawkins and M. Ridley (Eds.), Oxford Surveys in Evolutionary Biology (Vol. 2, pp. 1-27). New York: Oxford University Press.
1. This example obviously needs more elaboration. However, it is included here only as a means of illustrating the conceptual points being made.