Y chromosome evolving faster than the rest of the genetic code? What will result?

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Thursday 14 January 2010 | Science News feed

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Male chromosome evolving fastest, study shows
The Y chromosome is evolving far faster than the rest of the human genetic code, according to a study by scientists in America.

By Ben Leach
Published: 9:37AM GMT 14 Jan 2010

The research compared the Y chromosomes - which determine a man’s sex - from humans and chimpanzees, man’s nearest living relatives, and showed that they are about 30 per cent different.

That is far greater than the two per cent difference between the rest of the human genetic code and that of the chimpanzee’s. The changes occurred in the last six million years or so, relatively recently when it comes to evolution.

The gene test "The Y chromosome appears to be the most rapidly evolving of the human chromosomes," said Dr. David Page, the co-author of the study and director of the Whitehead Institute in Massachusetts.

"It's an almost ongoing churning of gene reconstruction. It's like a house that's constantly being rebuilt."

But the authors of the study, which appears in the journal Nature, said that just because the Y chromosome is evolving fastest it doesn't necessarily mean men themselves are more evolved.

Researchers took the most detailed examination of the Y chromosome, which females do not have, of both humans and chimps and found entire sections dramatically different.

There were even entire genes on the human Y chromosome that weren't on the chimp, according to the scientists

I understand the facts and concept, but I'm wondering how this shows up or is actually manifested in our species.

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But the authors of the study, which appears in the journal Nature, said that just because the Y chromosome is evolving fastest it doesn't necessarily mean men themselves are more evolved

Specifically, if the Y chromosome evolving faster doesn't affect the evolution of males - what does it mean? How does this phenomenon manifest itself? Is there any outward sign at all?

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@aidan,

Perhaps there will be some marked differences between males and females in morphology. Its quite common in birds and insects , its called sexual dimorphism (and sometimes trimorphism).

Its funny that the entire phenom in "Close ENcounters..." was a civilization where sexual polymorphism was common.

REMEMBER also, genes arent a CAUSE of evolution, they are the "bookkeeping" of evolution, so perhaps weve already expwerienced the morphological differences between the sexes. All weve gotta do is compare and list the differences between us and say, chimpanzees.

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@farmerman,

Yes, that's what I was wondering. If we compare male humans to male chimpanzees are there differences that are more pronounced than when we compare female humans to female chimpanzees, given that the Y chromosome has evolved faster, and in fact, contains genetic information in the human that is not even present in the chimpanzee?

And can or should we extrapolate from this that, because it is not mentioned that the same is true of the X or female chromosome, that the females of both species are more similar to each other than the males? Or is this an overstatement or misdirected conclusion?

I just find it extremely interesting, yet confusing (because I don't really know how to think it through logically to a conclusion) that males and females in the same species seem to be evolving in divergent ways and at different rates from what is believed to be a shared origin.

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@aidan,

Given the short time period involved, it might be a bit misleading to say the "Y" chromosome has "evolved" disproportionately, and it might be more accurate to say that it has accumulated more variation over time. It's unclear how much natural selection has altered the range of diversity.

As FM says, the result should ultimately be greater sexual dimorphism. As far as "what will result" is anyone's guess, but we might be able to anticipate by asking "what selection factors are (and have been) imposed on human males which alter their ability to produce children"?

For example, selection by women might lead to an increase or decrease in particular traits, although I'm not sure what that would be. Also, the likelihood of survival to a reproductive age would be a selective factor. Also, the probability of keeping your own children alive to a reproductive age would be a factor.

Also remember that "goodness" or "badness" of a male isn't a factor to evolution (unless it alters selection), all that matters is how many viably reproductive offspring he can generate. I've read that Ghengis Kahn was pretty good at getting his genetic code out there, even though his methods would not be approved of by modern society (or even society in his time).

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The fun thing for me is watch as science changes, the Y chromosome was considered for several years to be on the way out, that, in a couple of hundred thousand years, it wouldn't be a neccessary part of procreation. Now, this new look will change that idea.

Another quickly disappearing idea is that there is any such thing as 'junk DNA'. Farmerman's analogy to the genes being the bookkeeping on evolution is right on the money. All that 'junk DNA' I think we will find records the efforts and adventures we as a species have had along the way from tree-top to Laz-E-Boy Recliner.

Joe(what a long, strange trip it's been.)Nation

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Do Chimpanzees stop to ask for directions?

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Why would mutations - evolution - of the Y chromosome produce greater sexual differences? If anything, the phenology has been trending towards men being more effeminate.

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@littlek,

In this article they haven't spoken about any outward manifestations. That's why I was asking what they might be.

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If anything, the phenology has been trending towards men being more effeminate.

This is a species-wide phenomenon, not brought about or influenced by individual cultures as opposed to evolutionary or genetic changes?

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@littlek,

Not greater divergence from females, greater divergence from it's original form.

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@rosborne979,

Ah.

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@littlek,

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If anything, the phenology has been trending towards men being more effeminate.

What do you mean by that? Is there some way to measure effeminateness?

((scratches self and puffs up chest))

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@ebrown p,

men, in particular young men, are softer and rounder. It's been attributed to BGH in milk and less activity.

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@littlek,

Looks like I'm talking out my ass again.

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but a very nice ass it is... if you need to be talking out of it.

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@littlek,

littlek wrote:

men, in particular young men, are softer and rounder. It's been attributed to BGH in milk and less activity.

Less activity definitely leads to being softer and rounder. I can attest to that.

But it's not genetic. And unless women start to select softer and rounder men to have babies with, then no genetic predisposition for that will ever accumulate in the genome.

Which makes me wonder... IF women could guide the evolution of the Y chromosome by sexual selection, what would they select for?

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Women as a group...? I dunno. I think strong and healthy still mean a lot. But, with modern medical and scientific achievements, do they mean as much as they used to? What about the tech-savy factor?

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@littlek,

Tech savvy? Women are always impressed when I tell them about my Bayesian algorithm for pruning n-grams.

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@ebrown p,

Remember that the Y chromosome is transferred in semen and is store in the testes. The testes are an oxidative environment so the rate for mutation would probably be statistically higher.

Looking at it a nother way, the Y chromosome, by its extreme mnutability is actually unable to act as a major transfer of genetic information except , probably, by genetic drift (if a male offspring actually results) . Otherwise, any sexual dimorphism would arise from the X chromosome side.

Just a thought, dont quote me but Ill discuss it if it sounds too unrealistic.

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@farmerman,

That doesn't sound correct to me Farmerman.

All chromosomes (from one side of the exchange that is) are transferred in semen and stored in the testes. There is nothing special about the Y chromosome in this regard.

The implication half of the genes of any individual are too unstable to transfer genetic information seems unrealistic.

I suppose it is logically possible that this is the case, the implication being that males are a primary source of mutation and females provide stability,...but it doesn't seem likely.

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@farmerman,

Okay, this is what I was after because as I've said many, many times, although I find science very interesting, I was intimidated very early on in my science education to the point I never pursued it to the extent I should have. I was steered and allowed myself to be steered in a different direction more in step with my academic strengths.

But I do find it very interesting. So I will ask a lot of questions. I hope no one takes that as me challenging their responses. It's just the way I clarify things in my own mind for myself.

So- my first reaction to this:

Quote:

Remember that the Y chromosome is transferred in semen and is store in the testes. The testes are an oxidative environment so the rate for mutation would probably be statistically higher.

was to say, 'Oh, alright...' because I didn't specifically know about the more oxidative environment.
But then I thought, why would the semen be stored in an environment that could potentially produce more mutations?
Is there an evolutionary concept that would explain why that would be beneficial or necessary as opposed to garnering a net negative?

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Y chromosome evolving faster than the rest of the genetic code? What will result?

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