Evolutionary Psychology and the Problem of Neural Plasticity

Abstract

Evolutionary psychology as commonly presented is committed to the view that our cognitive architecture consists of a set of genetically pre-specified, domain specific, computational modules that are adaptations to the environment of our Pleistocene ancestors. These commitments yield a picture in which the underlying computational design of the human mind is genetically transmitted while cultural variation results from differential experiential inputs being processed through this common architecture. This view has been criticized from a developmental point of view. This paper develops some of those criticisms specifically as they relate to the plasticity of neural structures and their responsiveness to social interactions. My criticism is directed at common Evolutionary Psychologists’ arguments for the claim that the basic features of human cognitive architecture are adaptations to the environment of our Pleistocene ancestors, the so-called EEA. In best case scenarios the confirmation of adaptive hypotheses involves identifying the specific causal mechanisms of selection. This is not possible in the case of Evolutionary Psychology. Instead claims that certain computational modules evolved as adaptations in the ancestral environment are supported by their cross-cultural occurrence in modern populations together with their apparent complex design. However, evidence suggests that behavior itself, and cultural practices, influence the development of neural structures and the cognitive processes they instantiate. In this paper I review evidence of the effects of culturally-mediated behaviors on cognitive architecture, specifically the effects of literacy and musicianship. These examples are of interest because they are most likely cultural practices that have developed since the Pleistocene. This evidence suggests possible alternative explanations for the presence of complex cognitive mechanisms aside from the Evolutionary Psychologists claim that they must be adaptations to the EEA. In other words, there is some reason to believe that our cognitive architecture differs in significant ways from that of our Pleistocene ancestors due to the effects of culturally-mediated neural plasticity. According to this alternative view, while genes are playing a role in the development of the brain, they do not really encode its neural architecture. When selection favors one set of neural characteristics over alternatives, the genes that played a role in the development of those structures are passed on. But this does not guarantee replication of the structures themselves. What is being selected? Not genes, but organisms with certain neurological and behavioral tendencies in particular environments. Variation in the genetic determinants of neurological structure is not a necessary condition for natural selection to act on behavior. The necessary condition, as Darwin originally put the point, is that traits are heritable. Certainly heritability implies some genetic transmission between generations. But heritability of neural structure requires more than a genetic determinant because neural structures are so plastic. Some regulation of the experiential environment in which those genes act is also necessary. This suggests that an adequate account of the evolution of behavior requires a multi-level approach that recognizes that gene action and social behavior are related by a kind of causal reciprocity. Such an account would be quite different than the Evolutionary Psychologists’ model of culture being layered over the top of an underlying cognitive computer that is genetically propagated.