Friday, 16 September 2005

Brain May Still Be Evolving

Evolution of the Female Brain
(Click to enlarge)

From the New York Times :
Two genes involved in determining the size of the human brain have undergone substantial evolution in the last 60,000 years, researchers say, leading to the surprising suggestion that the brain is still undergoing rapid evolution.

The discovery adds weight to the view that human evolution is still a work in progress...
No Kidding?
The new finding, reported in today's issue of Science by Bruce T. Lahn of the University of Chicago, and colleagues, 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 brain function in some way, the report suggests, and they are more common in some populations than others.
The Chicago researchers began their study with two genes, known as microcephalin and ASPM, that came to light because they are disabled in a disease called microcephaly. People with the condition are born with a brain much smaller than usual, often with a substantial shrinkage of the cerebral cortex, that seems to be a throwback to when the human brain was a fraction of its present size.
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. About 70 percent of people in most European and East Asian populations carry this allele of the gene, but it is much rarer in most sub-Saharan Africans.

With the other gene, ASPM, a new allele emerged 14,100 to 500 years ago, the researchers favoring a midway 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 is found at low frequency in some sub-Saharan Africa peoples.

The Chicago team suggests that the new microcephalin allele may have arisen in Eurasia or as the first modern humans emigrated from Africa some 50,000 years ago. They note that the ASPM allele emerged about the same time as the spread of agriculture in the Middle East 10,000 years ago and the emergence of the civilizations of the Middle East some 5,000 years ago, but say that any connection is not yet clear.

Dr. Lahn said there might be a fair number of genes that affect the size of the brain, each making a small difference yet one that can be acted on by natural selection. "It's likely that different populations would have a different makeup of these genes, so it may all come out in the wash," he said. In other words, East Asians and Africans probably have other brain-enhancing alleles, not yet discovered, that have spread to high frequency in their populations.
There is so much about our species that we haven't discovered yet.

Meanwhile this particular Brain appears to be doing her own evolving, in a somewhat unusual but highly enjoyable fashion.

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