Posts within the RSS feed will now be truncated. Since I occasionally write longer pieces, it is likely you’ll now have to “click through” to read the full post. If the ending of a post mystifies you, there is a good chance that it’s due to truncation, and not my being on some medications.
Finally, I feel guilty putting this post up without a great deal of content, so I’ll throw a thought out there triggered by discussion below on phenotypes in the Middle East: how many alleles which code for particular traits arose in the genetic background of population A only to move to fixation in population B? Lactase persistence in Europe may be a classic case of this, originating in Central Eurasian populations and later spreading to the Northwest European fringe, where the favored variant rose to near fixation. Here’s another possibility: the allele which codes for blue eyes in West Eurasian populations may have arisen outside of Europe, and moved into Europe through gene flow, and then been driven to fixation in the new environment. Often when people see someone with light eyes who is not European the presupposition is there has been European admixture, but it may be that a low proportion of individuals with the light eye variant around HERC-OCA2 has been the norm in Western Eurasia outside of Europe for a long time. Only in the European population did selection, or perhaps drift through population bottlenecks, recently drive the variant to near fixation around the Baltic. Anyway, I think that’s a plausible model,though someone who has looked at the haplotype in detail could no doubt disabuse me of the notion. I am inspired here by the ‘speed up’ model of human evolution, where large populations result in a greater mutational background from which natural selection can draw. Presumably with agriculture Middle Eastern populations exploded rather rapidly ~10,000 years ago vis-a-vis other groups in Western Eurasia. I now believe that a substantial proportion of the ancestry of modern Europeans and South Asians derives from a demographic expansion rooted in the Middle East (in combination with native substrate). Many of the traits diagnostic to Europeans and South Asians, and genetic alleles diagnostic to both groups, may then drive from the Middle Eastern newcomers, and not be due to deep local ancestry. This may be what occurred with R1b1b2.
Image Credit: George Baird.