Chimp DNA Mapped

Here's the big news of the day. they've mapped the chimp genome, and it turns out we don't share 98-98% but only 96% of genetic material. Well, could'a fooled me, given what I've seen in my lifetime.

Here's an interesting tidbit about the Y chromosome that I wanted to share:

But another aspect of the comparison has yielded insights into a different question, the evolution of the human Y chromosome. The new finding implies that humans have led sexually virtuous lives for the last six million years, at least in comparison with the flamboyant promiscuity of chimpanzees.

Some 300 million years ago, the Y chromosome used to carry the same 1,000 or so genes as its partner, the X chromosome. But because the Y cannot exchange DNA with the X and update its genes, in humans it has lost all but 16 of its X-related genes through mutation or failure to stay relevant to their owner's survival. However, the Y has gained some genes from other chromosomes because it is a safe haven for genes that benefit only men, since it never enters a woman's body. These added genes, not surprisingly, all have functions involved in making sperm.

The scientific world's leading student of the Y chromosome, David Page of the Whitehead Institute in Cambridge, Mass., has been seeking to understand whether the Y will lose yet more genes and lapse into terminal decay, taking men with it.

The idea of the Y's extinction "was so delicious from the perspective of gender politics," Dr. Page said. "But many of my colleagues became confused with this blending of gender politics with scientific predictions."

Two years ago, he discovered a surprising mechanism that protects the sperm-making genes. Those genes exist in pairs, arranged so that when the DNA of the chromosome is folded back on itself, the two copies of the gene are aligned. If one copy of the gene has been hit by a mutation, the cell can repair it by correcting the mismatch in DNA units.

The 16 X-related genes are present in only single copies. Dr. Page and his colleagues thought the chimpanzee genome might show how they were protected. To their surprise, they report in Nature, the protection was not there.

The chimp Y chromosome has lost the use of 5 of its 16 X-related genes. The genes are there, but have been inactivated by mutation. The explanation, in his view, lies in the chimpanzee's high-spirited sexual behavior. Female chimps mate with all males around, so as to make each refrain from killing a child that might be his.

The alpha male nonetheless scores most of the paternities, according to DNA tests. This must be because of sperm competition, primatologists believe - the alpha male produces more and better sperm, which outcompete those of rival males.
This mating system puts such intense pressure on the sperm-making genes that any improved version will be favored by natural selection. All the other genes will be dragged along with it, Dr. Page believes, even if an X-related gene has been inactivated.

If chimps have lost five of their X-related genes in the last six million years because of sperm competition, and humans have lost none, humans presumably had a much less promiscuous mating system. But experts who study fossil human remains believe that the human mating system of long-term bonds between a man and woman evolved only some 1.7 million years ago.

Males in the human lineage became much smaller at this time, a sign of reduced competition.

The new result implies that even before that time, during the first four million years after the chimp-human split, the human mating system did not rely on sperm competition.

Dr. Page said his finding did not reach to the nature of the joint chimp-human ancestor, but that "it's a reasonable inference" that the ancestor might have been gorillalike rather than chimplike, as supposed by some primatologists.

The gorilla mating system has no sperm competition because the silverback maintains exclusive access to his harem.

So amongst other interesting observations, it seems alpha-male is deep in our DNA. The socio-biologist inference seems to be that I must go and knock off some boss ape in Hollywood/somewhere for his harem apes and impregnate them all... Or not as the case may be. However, if monogamy is only 1.7million years old for us, no wonder we've still got major problems sticking to that plan. :)