Friday, November 29, 2013

Male chromosome is essential and evolves faster

NY Times columnist Maureen Dowd writes:
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?” ...

“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,” Dr. 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.’”

Dr. 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 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 Times’s 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.”
Dowd previously wrote a book titled Are Men Necessary? So I guess she thinks that she is an expert on the subject.

So the Y chromosome got smaller between 250M and 25M years ago, and for that she thinks men are unnecessary?

If she read her own newspaper, she would have learned in 2010:
A new look at the human Y chromosome has overturned longstanding ideas about its evolutionary history. Far from being in a state of decay, the Y chromosome is the fastest-changing part of the human genome and is constantly renewing itself. ...

The chimpanzee and human lineages shared a common ancestor just six million years ago, a short slice of evolutionary time. Over all, the genomes of the two species are very similar and differ in less than 1 percent of their DNA. But the Y chromosomes differ in 30 percent of their DNA, meaning that these chromosomes are changing far faster in both species than the rest of the genome. ...

In the Y, which originally had the same set of genes as the X, most of the X-related genes have disappeared over the last 200 million years. Until now, many biologists have assumed either that the Y chromosome was headed for eventual extinction, or that its evolutionary downslide was largely over and it has sunk into stagnation.

Dr. Page’s new finding is surprising because it shows that the Y chromosome has achieved an unexpected salvation. The hallmark of the Y chromosome now turns out to be renewal and reinvigoration, once the unnecessary burden of X-related genes has been shed.

“Natural selection is shaping the Y and keeping it vital to a degree that is really at odds with the idea of the last 50 years of a rotting Y chromosome,” Dr. Page said. “It is now clear that the Y chromosome is by far the most rapidly evolving part of the human and chimp genomes.”
I was surprised that evolutionists could be so wrong for 50 years. Males are under much greater selection pressure than females, so it stands to reason that the Y chromosome would be evolving faster.

A current New Scientist article says:
The defining genetic feature of maleness, the Y chromosome, contains only two genes that are absolutely essential for male function – at least in mice. ...

Until recently, many geneticists thought of the Y chromosome as a vestigial ruin full of decaying genes and doomed to evolutionary oblivion because, unlike all the other chromosomes, it lacks a second copy to serve as a backup when mutation strikes. However, the Y turns out to have other ways of repairing mutations, and recent evidence suggests that the chromosome has been relatively stable over the last 100 million years of evolution. However, most of its genes are involved in a single function, male reproduction.
Update: Dowd announced that she decided early in life that boys liked her better when she was nice, so she quit being nice.

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