Men might not 'become extinct' after all: Theory of the 'rotting' Y chromosome dealt a fatal blow

February 22, 2012 by Matt Fearer, Whitehead Institute for Biomedical Research
sex chromosomes
The two sex chromosomes from a human cell. Image: ©2003 Howard Hughes Medical Institute.

( -- If you were to discover that a fundamental component of human biology has survived virtually intact for the past 25 million years, you'd be quite confident in saying that it is here to stay.

Such is the case for a team of Whitehead Institute scientists, whose latest research on the evolution of the human confirms that the Y—despite arguments to the contrary—has a long, healthy future ahead of it.

Proponents of the so-called rotting Y theory have been predicting the eventual extinction of the Y chromosome since it was first discovered that the Y has lost hundreds of genes over the past 300 million years. The rotting Y theorists have assumed this trend is ongoing, concluding that inevitably, the Y will one day be utterly devoid of its genetic content.

Over the past decade, Whitehead Institute Director David Page and his lab have steadily been churning out research that should have permanently debunked the rotting Y theory, but to no avail.

"For the past 10 years, the one dominant storyline in public discourse about the Y is that it is disappearing," says Page. "Putting aside the question of whether this ever had a sound scientific basis, the story went viral—fast—and has stayed viral. I can't give a talk without being asked about the disappearing Y. This idea has been so pervasive that it has kept us from moving on to address the really important questions about the Y."

To Page, this latest research represents checkmate in the chess match he's been drawn into against the "rotting Y" theorists. Members of his lab have dealt their fatal blow by sequencing the Y chromosome of the rhesus macaque—an Old World monkey whose evolutionary path diverged from that of humans some 25 million years ago—and comparing it with the sequences of the human and chimpanzee Y chromosomes. The comparison, published this week in the online edition of the journal Nature, reveals remarkable genetic stability on the rhesus and human Ys in the years since their evolutionary split.

Grasping the full impact of this finding requires a bit of historical context. Before they became specialized sex chromosomes, the X and Y were once an ordinary, identical pair of autosomes like the other 22 pairs of chromosomes humans carry. To maintain genetic diversity and eliminate potentially harmful mutations, autosome pairs swap genes with each other in a process referred to as "crossing over." Roughly 300 million years ago, a segment of the X stopped crossing over with the Y, causing rapid genetic decay on the Y. Over the next hundreds of millions of years, four more segments, or strata, of the X ceased crossing over with the Y. The resulting gene loss on the Y was so extensive that today, the human Y retains only 19 of the more than 600 genes it once shared with its ancestral autosomal partner.

"The Y was in free fall early on, and genes were lost at an incredibly rapid rate," says Page. "But then it leveled off, and it's been doing just fine since."

How fine? Well, the sequence of the rhesus Y, which was completed with the help of collaborators at the sequencing centers at Washington University School of Medicine and Baylor College of Medicine, shows the chromosome hasn't lost a single ancestral gene in the past 25 million years. By comparison, the human Y has lost just one ancestral gene in that period, and that loss occurred in a segment that comprises just 3% of the entire chromosome. The finding allows researchers to describe the Y's evolution as one marked by periods of swift decay followed by strict conservation.

"We've been carefully developing this clearcut way of demystifying the of the Y chromosome," says Page lab researcher Jennifer Hughes, whose earlier work comparing the human and chimpanzee Ys revealed a stable human Y for at least six million years. "Now our empirical data fly in the face of the other theories out there. With no loss of genes on the rhesus Y and one gene lost on the human Y, it's clear the Y isn't going anywhere."

"This paper simply destroys the idea of the disappearing Y chromosome," adds Page. "I challenge anyone to argue when confronted with this data."

Explore further: Chimp and human Y chromosomes evolving faster than expected

More information: "Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes" Nature, online February 22, 2012. DOI: 10.1038/nature10843

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5 / 5 (3) Feb 22, 2012
Only a fool will dare to argue with the facts established by the authors.
2 / 5 (12) Feb 23, 2012
I always thought the theory that the male chromosome would eventually die out was nonsense. Now it's proven [to be] nonsense.
2.2 / 5 (6) Feb 23, 2012
The Y could never disappear altogether. The essential genes driving the biological imperative preclude the patently illogical possibility of that chromosome disappearing.

Nature sought fit to equip those necessary genes with their own chromosome. The X has over 3,000 genes. The determination of the Y to stay around is expressed elegantly with the presence of an extra, supposedly superfluous Y chromosome, which renders the X completely dysfunctional.
3 / 5 (4) Feb 23, 2012
This must be devastating news to feminists, and Women's Studies.

2 / 5 (4) Feb 23, 2012
Take this lightly lol

Men have evolved throughout time and removed unnecessary genes which cause PMS, over talking, over emotions, over exaggeration, complication, etc

Sorry, it was too tempting =]
1 / 5 (3) Feb 23, 2012
But nonetheless a nest builder loves a hunter/predator for all sorts of dominant characteristics and play interaction reasons regardless of whether they are open to IVF or female to female relationships, not giving away any personal experiences of course...

Just to add, if we ever get the artificial wombs of the era of Dune (Frank Herbert) then men will still be around, though maybe in reduced numbers, to offer diversity as play things, so watch out, get fit, get smart and get networked and survive - or I will hunt you guys down and force you to eat Maccas for a whole year !
5 / 5 (1) Feb 23, 2012
YAY men!
1.8 / 5 (5) Feb 23, 2012
Aren't there some species where the y has disappeared and they still have two sexes with the determination being made by the father contributing either an x or no x?
3.7 / 5 (3) Feb 24, 2012
This must be devastating news to feminists, and Women's Studies.


Remember, if it doesn't align with their views it's not true. "How dare the sexist pigs who published this study say anything like that!"

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