Tuesday, October 09, 2007

Selection does a body   posted by Razib @ 10/09/2007 01:02:00 AM

The genetic architecture of normal variation in human pigmentation: an evolutionary perspective and model:
It has long been noted that the vast majority of the genetic diversity found in the human species is distributed within geographic populations...Only 5-15% is observed between groups, reflecting our recent origin less than 200,000 years ago. In contrast and intriguingly, an estimated 88% of the total variation in skin color is found among geographic groups...The discordance is probably the consequence of intense selective pressure in the past on important attributes of the skin, the organ that most immediately and extensively interfaces with our environments.

In terms of heuristics which allow us to filter and bias our perception of new data we look to the distribution of facts and processes which we know of prior. For example if I see that a trait is normally distributed and highly heritable I'm assuming that it hasn't been subject to a long period of strong direction selection, because that tends to eliminate the standing genetic variation necessary for these sorts of phenotypes. So you see two large geographic populations which are fixed for alternative alleles. Selection? Bottlenecks? Hitchhiking?