It’s really a rather pathetic-looking thing. The chromosome that makes me (and possibly you) male is a diminutive, asymmetrical thing next to the much larger, seemingly more complete X chromosome. I’m talking, of course, about the Y chromosome, part of the pair of chromosomes that determine our biological sex.
Last year, there were rumblings regarding the uncertain fate of the Y chromosome. To borrow a breathless Daily Mail headline: “The end of men? Expert predicts males will be extinct in five million years… and the process has already started!”
Very early in the evolution of the Y chromosome, explains Dr. David Page, a geneticist at the Massachusetts Institute of Technology, something pretty dramatic happened: The ancestral Y lost most of its genes. And scientists basically ignored the little that was left.
“The Y chromosome was essentially written off as the runt of the human genome,” Page says, “as a sort of genetic wasteland that didn’t really merit anyone’s serious attention.”
Part of the reason for this is that the Y chromosome, unlike every other chromosome in humans — including the X — is not paired. It has no partner, no fail-safe with which it recombines to weed out harmful mutations. The Y chromosome has been in a battle of attritition against the vagaries of mutation and it seems to have been losing. Which is where the “end of all men” shtick comes into play.
When the Y did get any attention, it wasn’t good news. Some scientists, like geneticist Jennifer Graves at La Trobe University in Melbourne, Australia, speculated that the Y might be destined to just keep sort of … rotting away.
“As soon as it becomes a male-determining chromosome, then the rot sets in,” Graves says. “That’s kind of the kiss of death for that chromosome,” meaning the Y chromosome could be headed toward oblivion — completely disappear.
Now, as Razib Khan pointed out last year in his blog post on this topic, this sort of radical extrapolation is more than a bit foolish. It also assumes a linear path for the Y chromosome, something Khan showed is not so by pointing to some research that catalogs just how varied the recent evolution of the Y chromosome is in several different groups of mammals.
In his piece, Stein gives the floor back to Page to ‘defend the honor’ of the Y chromosome:
Page has done a detailed analysis of the chromosome’s evolution and says the string of genes has been solidly stable now for millions of years.
“The idea that the Y chromosome might disappear altogether, possibly taking men with it — I think that idea has now been firmly dismissed,” he says.
Furthermore, the Y chromosome could be far more important than anyone expected, serving as a ‘master regulators’ throughout the body, Page says. But, as Stein sharply notes, there’s a catch:
Even if the Y chromosome is here to stay, that may be something of a double-edged sword for men. Even if those master genes on the Y chromosome are important, they may also help explain why men are more prone to certain diseases than women are — and tend to live shorter lives.
The rumors of the death of the Y chromosome appear to have been greatly exaggerated; it seems rather we are witness to the birth of a new appreciation of the complexity of this lumpy little bit of genetic material that carries so much freight in our culture.
Kenrick Vezina is Gene-ius Editor for the Genetic Literacy Project and a freelance science writer, educator, and naturalist in the Greater Boston Area.