Recently, I became interested in Evolutionary Psychology, specifically a research program proposed by Leda Cosmides and John Tooby. Cosmides and Tooby propose several principles for their research program (I will mention a couple): (1) The mind is a computational system organized into many domain-specific modules, (2) These modules are adaptations to adaptive problems during the Pleistocene environment. Obviously, what follows from (2) is that these modules are naturally selected and then passed on to offsprings through reproduction. What makes this research program appealing to me is that it incorporates Computational Theory of Mind into an Evolutionary (or an adaptationist) framework.
Despite this appeal, Evolutionary Psychology remains controversial, especially among Evolutionary Biologists and Philosophers of Biology. One of the main objections is whether or not Evolutionary Psychology is testable. After all, it’s very easy to come up with any untestable story about how some module became an adaptation via natural selection. However, there is another objection that some people think is a deadly blow to Evolutionary Psychology: Neuroplasticity. Why would anyone think that Neuroplasticity counts as a counter-example to Evolutionary Psychology?
Evolutionary Psychology states that the mind is massively modular and these modules are adaptations via natural selection. What these claims seem to imply is that if these modules are heritable adaptations, then they are stable or fixed features of the mind resistant to influences from the environment. However, Neuroplasticity seems like an example in which the modules are not fixed or stable features of the mind. Consider the specific example of Hemispherectomy. In some cases, hemispherectomy patients retain most of their cognitive functions despite losing one of their cerebral hemispheres. The remaining hemisphere reorganizes itself to perform cognitive functions normally performed by the missing hemisphere. So, perhaps modules are not stable features of the mind.
However, I don’t think Neuroplasticity counts as a genuine counter-example to Evolutionary Psychology. I think the reason why some people think otherwise is because of two reasons. First, people initially understand modules to be localized physical features of the brain. On the contrary, modules are distributive features of the brain individuated by their domain-specific functions (see Peter Carruthers’ Philosophy of Psychology). So, even if the localized features of the brain changes, the distributive features that implement domain-specific functions remain intact.
Second, people forget the distinction between the physical implementation of domain-specific functions and the domain-specific functions. This distinction is important because while physical implementations are plastic it does not follow that domain specific functions are plastic. Just because you can implement a software in a different hardware, it doesn’t follow the the software radically changes. In other words, domain-specific function X may originally be implemented by some distributive feature Y, but its implementation changes from Y to Z. So, Y no longer implements X, but Z implements X. What is implementing the domain-specific function changes, but the domain-specific function remains intact. So, perhaps Neuroplasticity (specifically Hemispherectomy) only shows that the physical implementations are plastic, but not necessarily the domain-specific functions.
To sum up in a crude manner, Neuroplasticity only shows that the hardware is plastic, but the software remains stable. Domain-specific functions can be implemented in several ways via neuroplasticity, but they remain domain-specific. Someone may deny domain-specificity and this is fine. The purpose of this blog entry is not to argue that domain-specific modules exist. Instead, its purpose is to argue how Evolutionary Psychology is compatible with Neuroplasticity.