The frequency of the gene increases because people who carry these genes are more fit and they have more kids. We think each gene conveys some sort of fitness advantage in brain biology. It could be an improved cognitive function or a personality trait. We're not sure. But we know whatever consequence they render is highly favored by selection.
More Quotes from Bruce Lahn:
My concern is that this is going to become justification for prejudices against certain groups.Bruce Lahn
If we look at multiple genes, the ethnic variations--such as the ones we found--are likely to be counterbalanced by other differences. It just happens that we looked at two genes for which the variants favored by selection have a higher frequency in some populations, such as Europeans. It might be that for the next two brain size genes we find, the variants favored by selection will have a higher frequency in Asians or Africans.
Bruce Lahn
The jury is still out on what this means because we aren't entirely sure what these genes do. It's possible they just control size and shape of the brain, rather than cognition. But the data is pretty compelling that the brain is evolving.
Bruce Lahn
I think a lot of people might consider humans to be at the pinnacle of evolutionary lineage -- that we have achieved an advanced state as a species, and we have basically become the end-game. But what we found indicates that the species -- particularly when it comes to the brain, which is perhaps our most defining feature -- is still evolving.
Bruce Lahn
They may have arisen in Europe or the Middle East and spread more readily east and west due to human migrations, as opposed to south to Africa because of geographic barriers. Or, they could have arisen in Africa, and increased in frequency once early humans migrated out of Africa.
Bruce Lahn
In a very short period of time, this class of variants arose from a single copy to many copies. That implies that this must have happened because of positive selection.
Bruce Lahn
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