Evolution of the Brain

Evolution was certainly the most powerful force in the long-term development of the human brain, but how much can "evolutionary psychology" (henceforth evo-psych) really help us understand brain functioning? It is appealing because of its frequent support of common intuitions, its succinct and seductive logic, and an abundance of neatly-packaged explanations for any human behavior. But all too frequently, evo-psych is filled with unfalsifiable and non-mechanistic just-so stories based on misconceptions and statistical half-truths. Just as the "intelligent design" movement emerged as "creation science" failed, so too has evo-psych attempted to restate the failed claims of sociobiology.

As Steven Rose writes in "The Future of the Brain: The Promise and Perils of Tomorrow's Neuroscience," "... like their predecessor sociobiologists, a group of highly articulate over zealous theorists have hijacked the term evolutionary psychology and employed it to offer yet another reductionistic account in which presumed genetic and evolutionary explanatations imperialise and attempt to replace all others. For evolutionary psychology, minds are thus merely surrogate mechanisms by which the naked replicators enhance their fitness. Brains and minds have evolved for a single purpose, sex ... and yet in practice evolutionary psychologists show as great a disdain for relating their theoretical constructures to real brains as did the now discredited behaviorist psychologists they so despise." As Steven Rose eloquently points out, evo-psych is fundamentally non-mechanistic: it purports to explain the "why" but never the "how" of brain function.

Further, most of evo-psych's claims are built on hunter-gatherer societies, of which we have little direct knowledge. This theoretical basis is problematic, given that as many as 11,000 generations could have elapsed between now and the Pleistocene era, commonly seen as the last great period of human evolutionary change. To further complicate matters, recent reprints of classic evo-psych papers that described the behavior of tribal cultures show that many of these "adaptive" or "universal" behaviors aren't even stable over a 20-30 year period. This incredibly plasiticity of human behavior, preferences and tendencies causes serious problems for any attempt at evolutionary logic.

Similarly, David Buller has debunked the common explanation of age-asymmetries in sexual relationships, which is that men have evolved to prefer women in their peak reproductive years, while women evolved to prefer high-status men. However, the data supporting this claim is ambiguous, in that other factors such as appearance and closeness in age explain equal or greater variance in mate selection as reproductive potential. Buller also shows, in contrast to popular evo-psych explanations of child rearing, that households with no genetic parents have the lowest incidence of abuse.

As noted by David Bullers' "Evolutionary psychology: the emperor's new paradigm," even Buss's classic work on the gender differences in sexual jealousy (females rank emotional over sexual fidelity, while males rank sexual fidelity as more important than emotional fidelity) is based on altogether questionable data. For one, the data do not actually show that males care more about sexual infidelity than they do emotional infidelity - in fact, over half chose the opposite response. Only a very narrow interpretation of the results supports Buss's original claims.

In summary, evo-psych has made minimal positive contributions to understanding the brain, and often buttresses claims that are unsubstantiated by experiment or real data. In other cases, the claims are simply unfalsifiable. However, given the intuitive appeal of evo-psych's logic and its widely-reported "findings," it's unlikely to disappear any time soon.


Anonymous Tim said...

I'm not sure if you read Mixing Memory, but Chris from there has posted several critiques of evolutionary psychology also. Worth a read if you haven't seen them -- The first one is here.

1/12/2006 03:02:00 PM  
Blogger Chris Chatham said...

Hey tim - yeah, I saw Chris's critiques after I wrote this post; I actually considered not posting this one simply because Mixing Memory covers many of these same criticisms so effectively!

1/12/2006 03:21:00 PM  

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