Commentary: Scientists ask, 'Why the Y?
CAMBRIDGE, Mass. — Even sitting in an MIT classroom made me feel smarter.
But I was still struggling with the difference between meiosis and parthenogenesis.
Dr. David Page, the zippy evolutionary biologist teaching a class Wednesday called “Are Males Really Necessary?,” had helpfully laid out some props to illustrate gene swapping — bananas, apples and heads of lettuce arranged on a table covered with a flowery white tablecloth.
“Since only females can give birth, why is it of any advantage to the species to have a second sex?” he asked. “Why should nature bother with males?”
He told the packed classroom about the ingenious genetic feat of the Laredo striped whiptail lizards in the Rio Grande Valley in Texas and Mexico.
“This species is a Girls Only club, and the girls reproduce by cloning themselves,” Page said. “In the species with males, life is pretty routine. The females produce eggs, the males produce sperm, fertilization occurs and the male-inclusive life cycle is completed. In species without males, life has a different texture. The females produce eggs, but the eggs do not need sperm. That’s parthenogenesis, which is a big word that means we understand absolutely nothing about how this works.”
He said old-fashioned fertilization (meiosis) beat cloning (parthenogenesis) because, as genes mutate, “males provide females with spare parts.”
It had been eight years since I’d talked to Page, director of the Whitehead Institute for Biomedical Research, about doomsday predictions that we were hurtling toward a planet without men in a mere 100,000 to 10 million years.
The Y chromosome was shedding genes and wilting into a mere remnant of its once mighty structure. Y declinists were arguing that, from sperm count to social status, men were vanishing, Snapchat-style.
The Y had shrunk to a fraction of the size of its partner, the X chromosome. (Obviously, Stephen Colbert told Page, it had just gotten out of the pool.)
The Y-sky-is-falling predictions mirrored Hanna Rosin’s thesis in “The End of Men,” showing that women are consolidating power — as graduates, breadwinners, single mothers, consumers.
Indeed, former Clinton money guy Terry McAuliffe would not be the new governor of Virginia if his Republican opponent, Ken Cuccinelli, had not scared off single women by belonging to a state party crew that was chasing women around with wands, trying to do transvaginal probes.
Even back when I first talked to Page — known as Mr. Y — he cast himself as “the defender of the rotting Y chromosome.”
He painted a picture of the Y as “a slovenly beast,” sitting in his worn armchair, surrounded by boxes and pizza crusts.
“The Y wants to maintain himself but doesn’t know how,” he said. “He’s falling apart, like the guy who can’t manage to get a doctor’s appointment or clean up the house or apartment unless his wife or girlfriend does it.”
But, as it turned out, it was a mistake to underestimate a chromosome that had for centuries madly attacked, annexed, enslaved, pillaged, plundered and thrust forward to create great art, architecture and literature.
Driven no doubt by lust and ego, the Y heroically revived.
“The Y chromosome did essentially fall asleep at the wheel about 200 to 300 million years ago, not long after we parted evolutionary company with birds, while we were still pretty close to our reptilian ancestors,” Page tells me now. “And then, at the last minute before the car veered off the cliff, the Y chromosome woke up and got with the program and said, ‘I don’t have a lot left, but what I have left I’m going to keep.’”
Page and Dr. Jennifer Hughes led a team that decoded the Y chromosome of rhesus monkeys, which share a common ancestor with humans, and discovered that the Y’s gene shedding leveled off about 20 million to 30 million years ago. In the Y’s cliffhanger, the chromosome used its toolbox to repair some of its genes and became fastidious about not allowing the other genes to be damaged.
As The New York Times’ Nicholas Wade sanguinely noted, “There are grounds for hope that the Y chromosome has reached a plateau of miniaturized perfection and will shrivel no more.”
While the Y was shrinking, the “buxom” X, as Wade dubbed it — formerly considered “a staid, pristine relic,” as Page says — was growing larger and stronger, acquiring new bunches of genes, some of which play roles in producing sperm.
But just when the Y thought it was safe to go back in the water, a new American study in the journal Science shows that mice, with only two Y chromosome-derived genes, can produce cells capable of joining with an egg to make a new mouse.
“Scientists have practically obliterated the ultimate symbol of maleness in DNA, the Y chromosome,” the BBC reported, “and believe they may be able to do away with it completely.”
Which brings us to a recent Sarah Silverman tweet: “Dear Men, Just b/c we don’t need you anymore doesn’t mean we don’t WANT you! Love forever, Women.”