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While the mammalian Y chromosome (males only) may be much smaller than the X chromosome that predominates in females (males have one X, females two), this males only chromosome is evolving much faster. As a result male primates were found to be evolving faster than females.  (Source:
The Y chromosome is evolving fast to deal with genetic pressures of varying mating habits, such as chimp group mating

Modern biochemistry and genetics is just beginning to unlock the complex secrets of evolution, the process in which organisms change over long periods of time through random genetic variation and selective pressures.  With a handful of genomes sequenced, scientists can now start mining this data to find interesting trends and evidence of the course evolution is taking, particularly in humans.

A provocative and intriguing new study reveals that past thought on the Y chromosome, the chromosome that instructs mammals to develop into males, may be entirely flawed and that the chromosome, previously thought to evolving at a crawl, may in fact be evolving far faster than other chromosomes.  Human females typically have two X chromosomes, while males have an X and a Y chromosome.

It was previously thought that autosomes (non-sex chromosomes) and the X sex chromosome featured greater diversity (faster evolution) than the Y sex chromosome, a smaller chromosome.  According to the new study, led by Jennifer Hughes, a postdoctoral researcher in Whitehead Institute Director David Page’s lab.  The research indicates that primate males may be evolving significantly faster than females.

To determine how fast the Y chromosome was changing, the scientists needed a point to compare our Y chromosomes against.  The human Y chromosome had been comprehensively sequenced by the Page lab and the Genome Center at Washington University in 2003.  A promising target was DNA from chimpanzees -- a close relative of humans on the evolutionary tree.  However, the 2005 sequencing of the chimpanzee genome excluded the Y chromosome, mostly, due to its hundreds of repeating sequences that threw off sequencing techniques at the time.

Undeterred, researchers at the Page lab and Genome Center at Washington University completed sequencing the chimpanzee Y chromosome, using newer techniques.  What was discovered was amazing.  The Y chromosome, thought to be a musty unchanging stretch of genes had changed significantly between humans and apes in terms of structure and content.  Approximately one third to a half of genes found in the human version of the chromosome were lost in the chimp chromosome, since chimps diverged from humans in the evolutionary tree.

Professor David Page compares these changes to a constantly renovated home, stating, "People are living in the house, but there’s always some room that’s being demolished and reconstructed.  And this is not the norm for the genome as a whole."

Wes Warren, Assistant Director of the Washington University Genome Center, another top genetics expert, agrees that the findings are extraordinary, "This work clearly shows that the Y is pretty ingenious at using different tools than the rest of the genome to maintain diversity of genes.  These findings demonstrate that our knowledge of the Y chromosome is still advancing."

One thing that may be driving faster evolution of the male sex chromosome is differing mating habits between species.  Where as humans typically take a single partner during sexual intercourse, numerous chimpanzees often mate with a single female in a short time period.  Males who produce more sperm, or whose sperm is better at impregnating females will have a better chance at beating the other males' sperm and passing on his genes.

To give an idea of just how profound this effect is, the difference between the rest of the human and chimp chromosomes is only 2 percent.  That means that the male sex chromosome is evolving nearly 15 times faster, or more, on average than the female genome.

The Page lab and the Washington University Genome Center are now looking at the Y chromosomes of several other mammals to further determine if this faster rate of male evolution is a characteristic of primates only, or other mammal lines as well. 

The study on the work was published in the prestigious journal Nature, and can be found here.

The research was funded by National Institutes of Health (NIH) and the Howard Hughes Medical Institute (HHMI).

Where as chimps have evolved to cope with the genetic pressures of group sex, human males and females have evolved on a different course.  Recent research indicated that human females are slowly evolving to be shorter and to carry more weight.

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Guaranteed, women will take this to mean
By marvdmartian on 1/14/2010 10:44:31 AM , Rating: 3
I guarantee you that most women will take this to mean that they are already perfect (or nearly so), so do not need to evolve any further.....unlike men!

Go ahead, tell your significant other.....see what she comes up with!

By Seemonkeyscanfly on 1/14/2010 10:57:50 AM , Rating: 4
Gee, had not thought it that way... I was going to say, "No duhh... Every guy knows we are more advance then females." but I keep forgetting how twisted the female brain has become.

I wonder if this is also why I like females that are younger then me more then females that are older???

RE: Guaranteed, women will take this to mean
By Akrovah on 1/14/2010 12:25:58 PM , Rating: 2
Thats just reproductive instinct. In general once a female hits maturity her fertility only goes down. As a result the Male sex drive tends to slant towards younger women because they have a greater chance of reproduction.

RE: Guaranteed, women will take this to mean
By kattanna on 1/14/2010 12:46:56 PM , Rating: 5
Male sex drive tends to slant towards younger women because they have a greater chance of reproduction.

and here i thought it was perkier boobs

By Seemonkeyscanfly on 1/14/2010 6:10:56 PM , Rating: 5
I'm was leaning towards the nice tight a**, but I have to agree with a nice perky set of ta-tas... but now I know it's a reproduction thing... well what's the point? It takes all the fun away and makes it just sex... Next you'll tell me there is no Santa.

By quiksilvr on 1/15/2010 1:09:12 PM , Rating: 2
And tightness...too far?

By mattclary on 1/15/2010 8:19:15 AM , Rating: 2
I wonder if this is also why I like females that are younger then me more then females that are older???

No, the boobs are just perkier.

By chagrinnin on 1/15/2010 1:44:25 AM , Rating: 2
aaaand that's when you fling poo at her.

RE: Guaranteed, women will take this to mean
By Fracture on 1/15/2010 9:27:32 AM , Rating: 1
Actually, having 2 X chromosomes is Nature's "easy way out" for filling in the genetic code. It often can lead to in other species.

Think of it this way: either have a copy of the same boring DNA you already have (females) or have a fast-evolving booster to the X chromosome you had first (males).

RE: Guaranteed, women will take this to mean
By sld on 1/15/2010 12:03:55 PM , Rating: 2
It is not a copy. The X chromosomes contributed by the father and mother are obviously different.

By Fracture on 1/15/2010 3:29:08 PM , Rating: 2
Unless in the case of parthenogenesis, as I clearly stated. The resultant offspring would have copies of the mother's chromosomes.

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