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Australian genomics expert Dr. Jenny Graves of Australian National University is visiting New Zealand this week, giving a series of lectures about the "decline of the Y chromosome and the future of humankind." Among the arguments made by Graves, according to the press release and the handout prepared for Graves' talk, is the fantastic claim that "humans might separate into two different species" as the result of the Y chromosome's shedding of genes over evolutionary timeframe, and "how intersex individuals... could be the saviours of humankind." Whoa. Wow. Damn.
The story of the diminishing Y chromosome hit the news (or rather, Maureen Dowd's misleading NYT column) this past June, when Dr. David Page and his colleagues published a paper about the evolutionary history of Y chromosome (Nature, June 19, 2003). Most chromosomes come in pairs, which enables them to swap corresponding genes with one another and to keep damaged genes from being passed on through the process known as recombination. The Y chromosome however cannot do this because it does not meet up with another Y chromosome. Without recombination, damaged and dysfunctional genes have accumulated on the Y chromosome over the evolutionary time, resulting in the loss of legitimate genes. The human Y chromosome is said to have contained 1,500 genes in the distant past, but now only has about 40. Graves and others speculate that the Y chromosome could lose all of its genes in five to ten million years, a claim that appears scientifically sound.
Adding to this knowledge, Graves states: "As the Y loses its ability to carry traits between generations, other chromosomes have been picking up the slack. It is only a matter of time... until a different gene to cause maleness picks up from the where the Y chromosome leaves off. Some humans already have other mutations that mean their genetic sex does not match their physical characteristics. Such intersex people could be the genetic saviors of mankind once the Y chromosome fails entirely, and take over as a new species. But if several different new sex determination mechanisms evolved, humankind could separate into several different species that are unable to breed with each other." Are you following this logic? No? Neither are we.
It appears to us that Graves (like Dowd) is mistaking chromosomes for humans. It should be obvious that intersex people, regardless of chromosomal makeup or fertility, are members of the same species as everyone else. Intersex people are known to be born to humans, and mate with (that is, exchange genes with) other humans, when that is possible. Nor is intersexuality caused by a single gene or solely by the Y chromosome; it includes a wide variety of biological status that may or may not have anything to do with the anomaly of the SRY gene. Besides, we will certainly not see a situation where intersex individuals will only mate with other intersex individuals.
Over all, it seems that Graves' argument is either oversimplification of many factors that influence human sex differentiation, or a case of poorly executed analogy. We feel that the socially stigmatizing implication of suggesting that intersex people would become a "new species" outweighs any scientific merit this argument might have.
In support of her argument, Graves gives an example of another mammal that have already separated into two species: voles. "The male vole has lost its Y chromosome entirely and become two different species." We wonder if intersex voles played any heroic role in saving the voledom too. Go intersex voles!
We appreciate Dr. Lisa Weasel, the Assistant Professor of Biology at Portland State University, for her insights and expertise on this topic.
Posted by Emi on Sep 3, 2003