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Health

Evolutionary logic

Gene ExpressionBy Razib KhanJuly 20, 2006 7:07 AM

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Over at Darwin Catholic there has been some discussion of the human influenced evolution of dogs. Seed actually has it right, it is human influenced evolution. Some of the interpretation of the paper which showed an increase in the frequency of 'deleterious' alleles spin the results as suggesting that dogs are beyond the constraints of evolution. But, as I pointed out over at DC's weblog dogs are evolved toward their own special adaptations, and the lack of these adaptations in their wild cousins is not evidence that wolves carry "deleterious" traits. For me, the most fascinating case of dog evolution is the possibility that they can read human faces. Their wild cousins can not do this, and in fact, it seems that man's best friend is better at this then his closest relative, the chimpanzee. Now, we don't think that wolves are "unevolved" because they don't have the capability to read human faces, they obviously didn't need to in the past. Similarly, dogs do not need functional constraint, that is strong selection maintaining a fixed form of an allele, on many loci because it does not impinge upon their fitness. Not being able to read human faces, or doing the "puppy thang" very well does have a negative impact on their reproductive output. To analogize with humans, just because reheaded individuals have lost function on the MC1R locus, and so are rendered very fair and susceptible to skin cancers as well as hypersensitive toward pain, does not mean they are maladapted. Rather, when you move an allele out of its evolutionarily shaped background its fitness may shift, obviously evolution did not anticipate that thousands of years into the future Europeans would resettle at lower latitudes (remember that almost the whole of the United States is to the south of Europe). The same sort of logic in relation to fitness allows us to infer things which should allow us to interpret the historical record better. For example, DC observes the negative correlation between fecundity and high socioeconomic status in the contemporary period, but, it seems clear that this is a recent phenomenon, otherwise we would not crave high socioeconomic status vis-a-vis our peers. In fact, the historical record, as documented in Mother Nature by Sarah Hrdy, suggests that until the last half of the 19th century elite women in Europe were literally baby machines in relation to their social inferiors. Primogeniture resulted in the reality that the broad mass of society was derived in large part from elites past, while the lower and working classes barely reproduced themselves as their slots were taken over by the younger offspring of the fecund nobility and gentry (in some societies slaves and the lower classes were punished for reproducing!). Related: JP makes a similar point.

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