Scale-free gene spread?

I'd blogged recently about this recent research. I've since run across more recent articles which clarify the opinion of the researchers.

From http://www.msnbc.msn.com/id/9258970/:

For the microcephalin gene, the variation arose about 37,000 years ago, about the time period when art, music and tool-making were emerging, Lahn said. For ASPM, the variation arose about 5,800 years ago, roughly correlating with the development of written language, spread of agriculture and development of cities, he said.

From http://www.forbes.com/lifestyle/health/feeds/hscout/2005/09/08/hscout527858.html:

Lahn and his colleagues believe that, over time, human behavioral and cultural developments might go hand in hand with this type of genetic selection. The microcephalin mutation's first appearance coincided with the beginnings of man's development of art, music, religious practices, and complex tool-making techniques, the researchers point out. Similarly, the launch of the ASPM mutations occurred with the spread of agriculture, urban settlements, and the first record of written language.

The spread of the genes may also have followed the equivalent of preferential attachment in scale-free networks. The rise of human settlement would have increased the choices available with regard to mate selection; we do not pick our mates randomly. A power-law expansion may have given rise to early spread of the particular gene variants. If the social selection is strong enough, perhaps there doesn't need to be an actual advantage conferred by these particular alleles; they may be simply hitching a ride on a process of socially-induced evolution.