Friday, September 09, 2005

ASPM and MCPH1: big trouble from two little alleles

Two variants of genes suspected to be related to brain function show very different distributions in different ethnic groups, and show signs of having been subject to strong selection fairly recently in human history. Of course, one cannot directly conclude anything about effects on intelligence, but the implication is pretty strong that there are correlations between distributions of genes with phenotypical consequences beyond superficial traits like skin or hair color, and traditional conceptions of ethnicity. This was already known for genes related to certain diseases like Tay-Sachs or sickle cell anemia. For related posts, see here and here.

NYTimes: Two genes involved in determining the size of the human brain have undergone substantial evolution in the last 60,000 years, researchers say, suggesting that the brain is still undergoing rapid evolution.

The discovery adds further weight to the view that human evolution is still a work in progress, since previous instances of recent genetic change have come to light in genes that defend against disease and confer the ability to digest milk in adulthood.

The new finding, reported by Bruce T. Lahn of the University of Chicago and colleagues in the journal Science, could raise controversy because of the genes' role in determining brain size. New versions of the genes, or alleles, as geneticists call them, appear to have spread because they enhanced the brain's function in some way, the report suggests, and they are more common in some populations than others.

...They report that with microcephalin, a new allele arose about 37,000 years ago, although it could have appeared as early as 60,000 or as late as 14,000 years ago. Some 70 percent or more of people in most European and East Asian populations carry this allele of the gene, as do 100 percent of those in three South American Indian populations, but the allele is much rarer in most sub-Saharan Africans.

With the other gene, ASPM, a new allele emerged some time between 14,100 and 500 years ago, the researchers favoring a mid-way date of 5,800 years. The allele has attained a frequency of about 50 percent in populations of the Middle East and Europe, is less common in East Asia, and found at low frequency in some sub-Saharan Africa peoples.

More coverage here, including comments like the following:

What I love about this article is that we're starting to get to the bottom of the seemingly infinite regress of lies and obfuscations.

Note that

1) they can't call Lahn a racist (he's a Chinese ancestry HHMI investigator publishing in Science, for god's sake)
2) they can't say the genes weren't selected
3) They can't say all populations have equal frequencies of these alleles
4) ...and they can't even say that there is even significant overlap between all populations on this locus (a la lewontin's 85/15 fallacy)

So those are four biggies gone at the outset. As Lahn has (wisely) separated the psychometric arguments -- for now -- they also can't demagogue IQ. So that's another one down.

Goldstein threw up drift, but it was already demolished -- unlike baseless mumbling about spandrels, it is actually a testable hypothesis and makes quantitative predictions (e.g. linkage disequilibrium varies for things boosted by drift vs. by selection). So it was tested and rejected, as it was in the Ashkenazi Cochran/Harpending paper. Next?

Next up they say that maybe *this* ASPM variant had some anomalous non-brain related function, or that different populations might not all have the same frequency of this allele, but that they have different complements of alleles that all lead to exactly the same distribution of ability.


Anonymous said...

Larry Summers is avoiding this story like the plague.

Steve Hsu said...

Hmm... maybe he has the right alleles? :-)

Anonymous said...

The social constructionists are like chickens with their heads cut off: they'll run around flapping their wings for awhile yet, but sooner or later the dread truth will dawn.

Anonymous said...

The check covers everyone except North American people

Anonymous said...


"Coop366 said...

The check covers everyone except North American people"

I noticed that also. However, genetically speaking, North America (as it is represented today) is really comprised of all those groups that were discussed. One could argue that the Native American ("Indians") are omitted, but would they be "lumped in" with the South American Indians?

Anonymous said...

Genetic studies of human Brainsize have discovered two genes that when mutated can result in a small brain, or “microcephaly.” Globally the genes for this condition are young and high frequency haplotypes are “rare” in Africa. THAT IS, Africans are less likely to carry the genes that, when mutated, can result in smaller brains than other groups (Currat et al, 2006; Mekel-Bobrov et al, 2006).

Tobias (1970) compared 7 racial and national groups in a study on brain size, in which he reported that the brain size of American blacks was larger than any white group, (which included American, English and French whites) except those from the Swedish sub sample (who had the largest brains of any of the groups measured), and American blacks were estimated to have some 200 million more neurons than American whites.

Currat M., Excoffier L., Maddison W., Otto S.P., Ray N., Whitlock M.C., Yeaman S. Comment on ‘Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens’ and ‘Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans’. Science (2006) 313:172. author reply 172.

Mekel-Bobrov N., Evans P.D., Gilbert S.L., Vallender E.J., Lahn B.T. Response to comment on ‘Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens’ and ‘Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans’. Science (2006) 313:172.

Tobias, T.V. (1970). Brain Size, Grey matter and Race – Fact or Fiction? American Journal of Physical Anthropology 32:3-26

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