Whither the Y: The Male Sex Chromosome Is Not Disintegrating

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The "rotting Y" theory, which suggested a literal end of the male sex chromosome, has finally been debunked by a new study in Nature.

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Two years ago, The Atlantic's cover proclaimed the "End of Men" in a riveting story by Hanna Rosin. She noted that women, for the first time in United States history, outnumbered men in the work force. Females were trouncing males in university acceptances and academic performance. Parents were even selecting girls more often than boys when using science to determine whether their child would be an "X" or a "Y."

Rosin's story came in the wake of studies claiming the Y chromosome was literally withering away, losing genes so fast that a "rotting Y" theory emerged suggesting a literal end of the male sex chromosome within five million years. This is lightning quick in evolutionary terms.

"The Y chromosome is dying," proclaimed biologist Jennifer Graves of Australia's La Trobe University in a 2009 speech, "The Decline and Fall of the Y Chromosome, and the Future of Men."

Of course, the withering of Y quickly became a metaphor for what Hanna Rosin and others were observing and reporting: that the traditional male, with his biceps, bluster, and raging testosterone, may be on the road to extinction.

Men will not actually disappear if the Y slips into history. Instead, I suspect that we will evolve—into what, I'm not sure.

I'm okay with toning down the aggression and other less admirable traits of extreme maleness, but extinction seemed a bit extreme. This is why, being a Y carrier, I was relieved to read a recent study in Nature that the male sex chromosome might have stopped disintegrating.

This news came from a team of geneticists at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, led by the Institute's director, David Page, and geneticist Jennifer Hughes. They studied the Y chromosome in humans and in rhesus monkeys, and discovered that Homo sapiens have lost just one gene in the 25 million years since these two species shared a common ancestor.

"I think it should finally put an end to the speculation about the demise of the Y," Hughes said in a Nature news story about the paper.

The idea of the incredible shrinking Y takes us back 200 to 300 million years, when our mammalian ancestors carried a Y that was about the same size as the X, with roughly 1,400 genes. Today the Y contains a puny 45 genes, a loss of around 97 percent.

Scientists believe that this DNA shedding occurred because the Y alone among chromosomes doesn't come in pairs, which tend to protect against genes being lost. Paired chromosomes recombine with each other during reproduction to reduce the impact of genes that are deleted or mutated. This includes the X, which comes in pairs in women.

What's left on the dissipated Y is important, however, and includes a gene called SRY that at conception switches on the development of testes and a gusher of male hormones. It also produces sperm.

Beyond this, no one is quite sure what the Y does, particularly when compared to the mighty X, which is crucial in all of us for everything from seeing properly in color and producing tooth enamel to protection from various diseases. The X also makes men more prone to baldness. (Did we really need that one?)

More interesting, though, is the question raised by the refutation of the "rotting Y" theory as a metaphor for male decline. Will this mean that the talk and asides about the diminutive and shrinking Y will stop, and apologies issued?

For instance, last month an article posted on AlterNet charged that a fear of male irrelevance might explain the decidedly antiquated views about women touted by Rick Santorum and his ilk. To support her case, writer Lynn Parramore noted that the "the Y chromosome is in danger of extinction." (To be fair, she wrote this on the very day the Whitehead study was published, and undoubtedly had not seen it).

This didn't seem to concern Parramore, however, given her assertion that: "There's enough sperm stashed away in banks to promulgate the human race indefinitely."

I also know women who suggest with some frequency that their man's Y chromosome is misbehaving again at the slightest hint of aggression -- say, on the freeway when another Y cuts them off. Or when beer bottles are left out overnight. Or when a man admits that he did indeed buy that Harley-Davidson in the driveway.

Not all researchers agree with Page and Hughes about the enduring stability of the Y chromosome. Australia's Jennifer Graves still believes that the Y is doomed, and argues that the decline occurs in fits and starts, with periods of quick losses and other periods where the rotting slows down or stops.

If this is true, then what will human's do to reproduce once the sperm banks are drawn down to empty? Pro-rotters have an answer to that, too, suggesting that before the X and Y separated, animals found other ways of dividing themselves up into males and females.

A few mammals today, including mole voles of Eastern Europe and the Japanese Ryukyu spiny rat have already have lost their Y and probably use other genes to switch on "maleness." Other animals, including some reptiles, have their sex determined by temperature and other environmental factors.

"The Y could disappear tomorrow if another sex-determining gene were to arise on an autosome," Graves told Nature News. (An autosome is a non-sex chromosome.)

This suggests that men will not actually disappear even if the Y slips into history. Nor will men vanish entirely from the workforce or from universities. Instead, I suspect that we guys will evolve -- into what, I'm not sure.

And there is more good news coming from Page and Hughes of the Whitehead. In another Nature study in 2010 they found that the Y is the fastest evolving human chromosome, changing at a clip that is 15 times faster than, say, the X.

This suggests -- metaphorically -- that we may find out sooner rather than later what's in store for the male of our species.

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David Ewing Duncan is a journalist in San Francisco. He is also a television, radio, and film producer, and he has written eight books. His most recent e-book is entitled When I’m 164: The Science of Radical Life Extension, and What Happens If It Succeeds. More

Duncan's previous books include Experimental Man: What one man's body reveals about his future, your health, and our toxic world. He is a correspondent for Atlantic.com and the Chief Correspondent of public radio's Biotech Nation, broadcast on NPR Talk. He has been a commentator on NPR's Morning Edition, and a contributing editor for Wired, Discover and Conde Nast Portfolio. David has written for The New York Times, Fortune, National Geographic, Harper's, The Atlantic, and many other publications. He is a former special correspondent and producer for ABC Nightline, and correspondent for NOVA's ScienceNOW! He has won numerous awards including the Magazine Story of the Year from the American Association for the Advancement of Science. His articles have twice been cited in nominations for National Magazine Awards, and his work has appeared twice in The Best American Science and Nature Writing. He is the founding director of the Center of Life Science Policy at UC Berkeley, and a founder of the BioAgenda Institute. His website is www.davidewingduncan.com

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