Study Indicates Human, Chimp Males Evolving Faster than Females
January 14, 2010 10:40 AM
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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.
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
Professor David Page
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
, and can be
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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RE: Title is innacurate
1/14/2010 8:23:22 PM
Sounds like an attempt to be politically correct and unoffensive by the New York Times to me. Granted, just because men have evolved faster doesn't mean they still are, but it sounds to me like they were worried people would be offended because they would think that evolving faster is a good thing. It's totally neutral, really.
Divergent evolutionary paths between the two genders of a species is nothing new. Males and females of many species have different evolutionary pressures, not just based on the survival of the fittest, but also based on sexual selection - reproduction of the fittest. The fact that those different pressures have resulted in greater changes in male chromosomes than females doesn't mean that men are better than women; it's more likely that men weren't as suited to those pressures initially, and so have had the most need to evolve. Although it can't be ruled out that the double (triple?) duty that the X chromosome has to play has some effect on the total 'elasticity' of the cromosome.
This doesn't mean that the phenotypic expression of those genes necessarily favors males more than females, or that the evolution which has taken place is favorable to the modern human existence. In the end, it's interesting to know, but by itself, it has no real bearing on the fitness of each human gender to modern life.
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