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June 11, 2004

Degeneration of the modern?

A few weeks ago I read The Cooperative Gene by Mark Ridley. If you want to read a popular book that spends a lot of time on DNA repair, Ridley's the man for you!

But there is one part that I think might be of particular interest to GNXP readers:


...A review paper written in 1962 described 7,712 people from thirteen different 'traditional' societies, including hunter-gatherers or simple, non-traditional farmers, from Africa, Greenland and elsewhere, who had an average frequency in males of 2 percent. In contrast, 436,853 people from ninety-nine samples of 'wealthy' societies had a frequency of about 5 per cent...The 'wealthy' samples were mainly from European 'or ancestrally European' populations, but also from some East Asian societies...The frequency of the mutant genes that cause colour blindness appears, in rich nations in the mid-twentieth century, to have doubled from its ancestral level.

Ridley notes that using colour-blindness is a better metric than myopia for build up of mutations since the evidence for the latter's genetic component is more mixed. In any case, the gist of Ridley's point is that he is exploring the possibility of a mutational meltdown, and suggests that spontaneous abortions of unviable fetuses is purifying the genetic background enough to prevent this. Of course, he does not address different levels of fitness in the context of fecundity, which to my understanding has not been modelled as thoroughly.

In any case, what was the original review paper? I suspect it was Population differences in red and green color vision deficiency: a review, and a query on selection relaxation in Eugenics Quarterly. The author is listed as "POST RH," but in Ridley's bibliography, only a later paper published in 1971 in a different journal is listed for this author (on the same topic). Seems to be Ridley was conscious about a brand-name problem when he saw it, especially in light of his discussion of the inevitability of spontaneous abortions (miscarriages) approvingly as a process by which mutational meltdown is being headed off.

In any case, why does Ridley have to go back to the 1960s and 1970s to find these papers? Aren't these topics interesting anymore? Just as there has been relaxed selection among the populace of developed nations, surely there has been an increase of fitness for traits that might have been deleterious in the past, or for combinations of alleles.

Posted by razib at 03:28 AM