Sex, like vitamins, has no end of contradictory research findings. Not so long ago (two months?) it was common belief among scientists (if not among the female population) that males – in particular the Y chromosome – were degrading (evolutionarily speaking). Evidence seemed to show that the mammalian Y-chromosome is slowly deteriorating, or at least stagnant. You might remember headlines like, “Are Males Necessary?” (Such headlines seem to show up every now and again.) Now, a new study conducted by the Whitehead Institute (Massachusetts, USA) has reached a different conclusion: The Y-chromosome is quite active indeed, not degrading or static at all, thank you.
The basis of the study is a first-of-its-kind direct comparison between the Y-chromosomes of chimpanzees and human beings. There was a surprise. It was expected that the chimp Y-chromosome (arduously decoded for this study by the Genome Center at Washington University) would be almost identical to that of the human Y-chromosome. It’s not. The human Y-chromosome has 30-50% more genes than the chimp. Assuming that chimps and human started with the same genome, this change or ‘loss’ of genes on the part of chimps indicates that in a relatively short time (evolutionary time) the Y-chromosome has been quite dynamic.
Why has the chimp chromosome changed? We don’t know. The study speculates:
“People are living in the house, but there’s always some room that’s being demolished and reconstructed,” says Page, who is also a Howard Hughes Medical Institute investigator. “And this is not the norm for the genome as a whole.”
Wes Warren, Assistant Director of the Washington University Genome Center, agrees. “This work clearly shows that the Y is pretty ingenious at using different tools than the rest of the genome to maintain diversity of genes,” he says. “These findings demonstrate that our knowledge of the Y chromosome is still advancing.”
Hughes and Page theorize that the divergent evolution of the chimp and human Y chromosomes may be due to several factors, including traits specific to Y chromosomes and differences in mating behaviors.
Because multiple male chimpanzees may mate with a single female in rapid succession, the males’ sperm wind up in heated reproductive competition. If a given male produces more sperm, that male would theoretically be more likely to impregnate the female, thereby passing on his superior sperm production genes, some of which may be residing on the Y chromosome, to the next generation.
This is to say that sexual practices may, eventually, have some impact on sex chromosomes. The Y-chromosome, at least for chimps, is evolving even faster than the rest of its genome – static it’s not. This may also be true for humans, although it would be very hard to characterize anything in the range of homo sapiens sex practices as genetically advantageous.