Genes and Brains

The subject of genes and the brain is a kind of third rail in human biology. Any results become targets for racists who use them to promote their theories and for many of my fellow liberals who denounce the very idea of such research. But it's still too important to ignore.

Bruce T Lahn and colleagues have some papers in Science discussing recent genetic changes in genes that affect brain size. The Science papers are behind a subscription wall, but many of the points are summarized in Nicolas Wade's NY Times article. They considered some genes in a group which, in mutated form, produce microencephaly (very small brains). They focussed on two of these genes that have alleles (variants) that appear to have arisen recently and spread widely, implying that they have a strong selective advantage.

Besides the connection with microencephaly, there is another hint that the genes could be connected to brain size and intelligence. In earlier work, Lahn

showed that a group of 20 brain-associated genes, including microcephalin and ASPM, had evolved faster in the great ape lineage than in mice and rats. He concluded that these genes may have played important roles in the evolution of the human brain.

As usual, the problem arises because of the link to the controversial relation of race and intelligence:

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.

Let's start by mentioning one thing this study doesn't do: It doesn't show whether or not the allele in question promotes greater brain size or any aspect of intelligence.

It does seem to show that, for at least some populations, it gives some selective advantage, but whether it's more smarts, warmer feet, or whatever, we don't know.

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.

My "warmer feet" notion is of course just a silly invention of mine, but one could certainly see an advantage for all those populations who have lived in cold places, but not for sub-Saharan Africans.

The other gene, called ASPM, has an apparently much more recently invented allele.

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.

Since it arose about the same time as Agriculture, it's at least possible that there is a connection.

The obvious further work is to 1) Investigate the specific functions of the genes 2) See if the alleles correlate with brain size, intelligence, personality, or whatever (warm feet?)