September 9, 2005

John Hawks on Lahn's genes

Blogging anthropologist John Hawks of the U. of Wisconsin has a good overview of the two new papers by Bruce Lahn:

Some populations have these alleles at high frequencies; other populations have them at lower frequencies or not at all. The genes are slightly different in their pattern: for example, the [the roughly 37,000 year old] Microcephalin haplogroup D is virtually universal in New World populations; the [roughly 5,800 year old] recently-selected ASPM haplogroup D is almost completely absent there.

Presumably, that's because the older gene arose before the first Siberians crossed into the New World, while the newer one originated after main migrations across the Bering Strait had ended.

The selected ASPM variant is most common in Europe and West Asia and less so in East Asia; Microcephalin haplogroup D is common across Eurasia from west to east. These differences may reflect time -- with the ASPM variant much more recently selected. Or they may reflect different selective gradients: perhaps the alleles are adaptive in some ecological contexts or genetic backgrounds but not others.

Both selected alleles are relatively rare in subsaharan Africa. Again, one of two explanations is possible: either they are advantageous but haven't had time to increase in frequency there yet, or their adaptive value is less in Africa than in other places where they are found...

The question is whether there is anything keeping them from spreading through Africa. Is it possible that the ecology of Africa has led to a different level of selection on these alleles? Or have they just not had time since their origin to reach very far into Africa? At any rate, it is premature to say what their effects may be within different populations, particularly until something is known about the phenotypes of people who carry the alleles.

A test that might shed light on this question is whether or not these gene variants are common in areas in New Guinea and Melanesia that are ecologically similar to the wetter parts of tropical Africa.

My published articles are archived at -- Steve Sailer

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