Whither the Y: The Male Sex Chromosome Is Not Disintegrating

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.

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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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