Hey, guys! The scientists are on to us!
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Genes expose secrets of sex on the side
Men have been tomcatting around since time immemorial, and some
traveled far from home to do it, new research suggests.
And there's no covering up even ancient sexual dalliances: the guys
most successful in sowing wild oats passed on the proof in their genes.
By using those genetic smoking guns, researchers at the University of
Arizona in Tucson have developed new insights into ancient mating and
migration patterns in humans.
Men and women differed in their participation in reproduction, the
researchers report. More men than women get squeezed out of the mating
game. As a result, twice as many women as men passed their genes to
the next generation.
"It is a pattern that's built up over time. The norm through human
evolution is for more women to have children than men," said Jason
Wilder, a postdoctoral fellow in UA's Arizona Research Laboratories
and lead author on the research articles. "There are men around who
aren't able to have children, because they are being outcompeted by
more successful males."
Co-author Michael Hammer, a research scientist in UA's Arizona
Research Laboratories, said, "We may think of ourselves as a
monogamous species, but we're coming from an evolutionary history
that's probably slightly polygamous. If we're shifting toward
monogamy, it's so recent it hasn't left an imprint on our genome."
Or the same reproductive behavior is continuing, but in a culturally
accepted fashion, Wilder said. "The modern version that we generally
don't find offensive is that men tend to remarry and have more
children much more often than women do."
The team's research also overturns the long-accepted idea that, on
average, women's genes traveled farther from their birthplace than did
men's. That idea was based on a common marriage practice called
patrilocality, wherein women tended to move from their natal village
to their husbands' village.
If anything, men and their genes moved farther overall, the new
research indicates.
To sort out how far men and women's genes traveled, the UA researchers
used DNA from the Y chromosome, which is passed from father to son.
Women's lineages were traced using mitochondrial DNA, which passes
from mother to daughter.
The researchers report their findings in two related articles, one in
the online early edition of the October issue of Nature Genetics and
one in an upcoming edition of Molecular Biology and Evolution. The
research was funded by the National Institutes of Health.
Scientists have puzzled over the fact that men's common ancestor,
dubbed Y-chromosome Adam, seems to have lived around 100 thousand
years ago, whereas women's common ancestor, known as mitochondrial
Eve, lived almost 200 thousand years ago.
Worldwide, the DNA from the Y chromosome has much less genetic
variability than does mitochondrial DNA.
"We wanted to know what shapes the patterns of Y-chromosome and
mitochondrial DNA variation," said Wilder. "What can we learn about
human behavior?"
To find out, Wilder, Hammer and Zahra Mobasher, a research specialist
at UA's Arizona Research Laboratories, tested Y-chromosome DNA and
mitochondrial DNA from three far-flung populations of humans: the
Khoisan of southern Africa, Mongolian Khalks and highland Papua New
Guineans. For each group, DNA from 24 or 25 people was tested.
Previously, researchers assumed equal numbers of men and women
procreated. Based on that assumption, scientists explained the
relative youth and low variability of the Y chromosome by suggesting
that a beneficial mutation on the Y had swept through the whole world.
However, the genetic patterns the UA researchers found contradicts
those ideas.
If a beneficial mutation had swept through the males, men's common
paternal ancestor would be the same age no matter where the UA
researchers looked. Instead, the age of men's common ancestor differs
between the southern African, Mongolian and Papua New Guinean
populations studied. The finding tends to rule out some global
beneficial mutation as the reason Y-chromosome DNA is less variable
than mitochondrial DNA.
"Because we don't think the pattern we see was caused by an event that
swept across the globe, we had to re-examine our assumptions about
whether equal numbers of men and women are mating," Wilder said.
The team thinks the genetic patterns are all about sex.
Or lack thereof. Lots more men than women are childless, and it has
ever been thus, the researchers say.
To see whether men and women traveled equal distances while sowing
their wild oats, Wilder, Hammer and Mobasher teamed up with research
specialist Sarah Kingan and Maya Pilkington, a doctoral candidate in
UA's department of anthropology. The group tested DNA from 389
individuals representing 10 distinct human populations from places as
far apart as the Netherlands, South Africa and Papua New Guinea.
Previous explanations of women and men's migration patterns had been
based on a combination of genetic patterns and knowledge about the
marriage practice of patrilocality. About 70 percent of the world's
cultures practice patrilocality.
When populations are compared, patrilocality would predict greater
differences between populations in Y-chromosome DNA than in
mitochondrial DNA, which is just what earlier population genetic
research found. Patrilocality also predicts that, on average, men do
not migrate as far as women.
On the basis of the genetic work, women's rate of migration had been
pegged as eight times higher than men's.
The UA team didn't think local marriage practices could govern
global-level patterns of genetic variation. But variation in the
Y-chromosome is hard to study.
The researchers started looking at bits of the Y chromosome known as
the Alu family of retrotransposons.
"We found lots of Y-chromosome variations that people didn't know
exist," Wilder said.
The new technique revealed that Y-chromosome DNA and mitochondrial DNA
differ to the same degree among populations.
Hammer said, "That alone wouldn't say the Y chromosome is migrating
more, but if just half as many males are getting their genes into the
next generation on average as are females, then it implies more males
are migrating to do that."
The pattern the researchers see in our genes doesn't require mass
migrations of people across continents. The sailors with a girl in
every port could have done it. Or it may be that village women snuck
out for trysts with tall, dark strangers. Either way, Y chromosomes
got around.
researcher contact info: Jason Wilder, 520-626-1626,
jawilder@email.arizona.edu
Michael Hammer, 520-621-9828,
Michael Hammer's website:
http://lifesci.ibsb.arizona.edu/faculty.php?faculty_id=2891
http://www.eurekalert.org/pub_releases/2004-09/uoa-ges091604.php
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John Hachmann aa #1782
-The ability to change one's mind, ideas, and opinions when confronted with
new facts is the sign of the rational and intelligent. The inability to do
so is the hallmark of the dimwitted and the fanatic. This applies not only
to science and philosophy, but also to politics.-
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