In Defense of Evolutionary Psychology

Jerry Fodor's review of a recent book criticizing Evolutionary Psychology contains some good points, but also claims that Evolutionary Psychology is invalidated by its use of an argument that ought to be completely unnecessary. Fodor has one important major point: that we can't assume that the details of any trait were directly selected for and optimized by evolution. Selection pressure is simply not that strong, so we have a lot of traits that are by-products of other adaptations. An evolutionary explanation requires more than a just-so story. This is more or less the root of my own objection to Evolutionary Psychology as it's currently practiced -- it assumes that the details of modern behavior were directly selected for.

But Fodor confuses the issue by bringing in the strange notion that to say that a mental characteristic is an adaptation, there has to be something somewhere -- whether it's our own unconscious, or "mother nature," or whatever -- that "wants" us to maximize our reproductive success. He points out, correctly, that any behavior could have a plurality of motivations, and that to explain a behavior one must first identify the motivation, then explain why that motivation exists. According to Fodor, Evolutionary Psychology explains our ordinary motivations by appealing to a deeper motivation for reproductive success.

Obviously postulating the necessary existence of a desire for reproductive success lying behind every mental adaptation is silly. But it's also unnecessary. There's a tendency to slip into teleological language when talking about evolution, and Fodor cites some examples from Richard Dawkins and others. But a mental propensity can evolve on the basis of its contribution to reproductive success without anyone anywhere wanting to be reproductively successful. All it requires is that the propensity in question in inheritable and has, among its effects, that it leads to greater reproductive success than the available alternatives.

For this reason, evolution is entirely consistent with a plurality of motivations. Ceteris paribus, having lots of sex will lead to geater reproductive success than having less sex. Now, imagine a population in which some people have a gene that leads them to find sex distasteful, other people have a gene that makes sex lots of fun, and a third group has a gene that makes them believe that having sex will keep the moon from falling. And let's assume that genes 2 and 3 create motivations whose strength is such that they lead their holders to have the same amount of sex, whereas the people with gene 1 are motivated to have much less sex. In this situation, the people with gene 1 will fail to pass it on to their descendants, whereas genes 2 and 3 will each be passed on to an equal number of descendants. Within a few generations, there will be hardly anybody left with gene 1. But because genes 2 and 3 produce behaviors that are equivalent in terms of promoting reproductive success, they will continue to be passed on in equal amounts. Our population will have evolved two different motivations for sex, neither of which entails anyone or anything "wanting" anyone to have reproductive success. There are further questions to be asked about why it was genes 2 and 3 that were present in this population, as opposed to, say, gene 4 which would have also motivated people to have lots of sex. But to explain why genes 2 and 3 persisted while gene 1 did not needs to refer only to their behavioral effects, not to their content or to some unattached motivation for reproductive success.