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Not all universals are adaptations

Another caution we must always consider is that not all universals are necessarily adaptations. There just may not be an evolutionary story to tell about those universals. Or more precisely, it will always be possible to come up with some Just So Story to tell, but there won't be any correct one.

First we must recognize that not everything that is universal is innate. A well used example is the human navel. This is a human universal, which is arguably not innate. Another is that when we fall, we fall downward instead of upward. The second point is that some innate characteristics are not neccessarily adaptations. They may be side effects (even maladaptive ones) of design constraints. That we blink both eyes simulteneously instead of one at time is probably one of these. These sorts of by-products of design constraints is probably what [Gould and Lewontin1979] mean by ``spandrel''. [Dennett1995] discusses the difficulty with actually trying to pin down the spandrel argument. [Dennett1995] and [Cronin1991] argue that Gould and Lewontin may have been attacking a straw man, since no one seriously believes that all characteristics are adaptations. The real question is then about the boundries.

What characteristics should we expect natural selection to explain? The eye, the kangaroo's pouch, the human chin, the cheetah's sprint, the chameleon's camouflage? What about the peacock's tail, the bee's suicidal sting, the crimson of blood, the flash of colour on a bird's wing? Should we expect it to explain human altruism, our love of music, feelings of aggression, sexual jealousy? And divorce rates, wars, political oppression? What, in short, is the scope of natural selection? p. 81 [Cronin1991]

There will be consensus on some of these. The crimson of blood is not an adaptation in anyone's view, without weakening the notion of adaptation to the point of making it uninteresting. But after examining the general question, Cronin concludes (p. 110) that ``non-adaptive explanations cannot be treated as other than a last resort.''

Dennett, in his discussion of spandrels, comes to the same conclusion; but when he discusses human behaviors he takes the opposite view that we should first look at other explanations for a cultural universal before looking for an evolutionary one.

We need to look at each remarkable similiarity [of culture] in turn to see if any of them needs a genetic explanation, for in addition to cultural cross-fertilization (cultural descent) and chance, there is the possibility of reinvention. There may be specific genetic factors operating in many or all these similarities, but, as Darwin stressed, the best evidence will always be idiosyncrasies--quirky homologies--and no-longer-rational survivals. §16.4 [Dennett1995]

Dennett goes on to point out that some EPers have found exactly such ``quirky homologies'' which are best explained by evolution, but we do have a shift of the burden of proof onto the evolutionary explanation for facts about human society and culture. Dennett loves extreme examples:

[S]howing that a particular type of human behavior is ubiquitous or nearly ubiquitous in widely separated human cultures goes no way at all towards showing that there is a genetic predisposition for that particular behavior. So far as I know, in every culture known to anthropologists, the hunters throw their spears pointy-end-first, but this obviously doesn't establish that there is a pointy-end-first gene that approaches fixation in our species. §16.4 [Dennett1995]

We can't quite make sense of how Dennett supports his emphasized expression ``goes no way at all'', but the general point is taken. As Dennett himself says, the best work in EP does not look for pointy-end-first genes, but some of its supporters may start falling into that trap.

Not enough time and reflection has passed for anyone to be able to say whether the fruits of EP are poisoned or are from the tree of knowledge. That debate will continue. We are attracted to the study of human universals and working with scholars from a variety of disciplines. EP is where that is happening the most boldly, and we are enthusiastic; but wish to temper our enthusiasm with a great deal of caution.

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Next: More cooperation to come? Up: The case for the Previous: EPstay home

Mon Sep 8 18:21:39 BST 1997