Was Ardipithecus monogamous?
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 divergence 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 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 controversial conclusions that Ardipithecus was monogamous in its mating habits, though this point is not made by the authors of the Nature letter.
References
Hughes, F.; Skaletsky, H.; Pyntikova, T., et al. Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content, Nature 28 (663) 536-539 (2010).
Lovejoy, O. (2009): Reexamining Human Origins in Light of Ardipithecus ramidus, Science 326 74 (2009).