There was an interesting letter in Nature last week about a comparative study carried out between the Y chromosomes of humans and chimpanzees. The Y chromosome is one of the two sex-determining chromosomes in most mammals, containing the SRY (sex determining Y) gene, which triggers the development of male gonads. The primate Y chromosome is hundreds of millions of years old and given that chimps are so closely related to humans, one would expect to see little difference between the Y chromosomes of the two species. In fact the male specific regions (MSY) of the two show considerable differences, more consistent with a divergance time of over 300 million years rather than just 6 million years. The authors of the paper attribute the differences to the prominent role in sperm production of the MSY and to differences in mating behaviour between the two species. The heightened sperm competition in the chimpanzee lineage may account account for the changes; the paper suggests that by comparison the human MSY is little changed.
The implication is that the chimpanzee promiscuous mating strategy is the derived behaviour and the mating strategy of the human/chimp last common ancestor was more human-like than chimp-like. This in turn would support Owen Lovejoy’s controversal conclusions that Ardipithecus was monogamous in its mating habits, though this point is not made by the author of the Nature letter.
Hughes, F.; Skaletsky, H.; Pyntikova, T. et al (2010): Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content, Nature 28 January 2010 Vol. 663 pp 536-539
Lovejoy, O. (2009): Reexamining Human Origins in Light of Ardipithecus ramidus, Science 2 October 2009 Vol. 326 p 74