Mowing the Lawn Shirtless
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From: Peter Langston <psl>
Date: Wed, 4 Jun 97 22:51:58 -0700
Subject: Mowing the Lawn Shirtless
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Study: Those cheatin' chimps
There may be more monkey business going on among chimpanzees than scientists
A study suggests that half of all chimpanzees may be conceived on the sly
when females sneak off for risky trysts with males outside their social
Female chimpanzees' secret sex lives come as something of a surprise to
researchers, who previously thought that they almost always mated within
their own group of 20 to 100 animals.
"When they can get away with it, they sneak off and they try to expand the
pool of possible fathers," said Pascal Gagneaux, a professor at the
University of California at San Diego.
Working with UCSD biologist David Woodruff and Christophe Boesch of the
Basel Zoological Institute in Switzerland, Gagneaux painstakingly worked
out the genetic family tree of a chimpanzee group living in the Tai Forest
of West Africa's Ivory Coast.
Between 1991 and 1995, he and his colleagues collected DNA samples >from
all 52 members of the Tai Forest group. The DNA came from hair -- collected
from chimpanzee sleeping nests by researchers who climbed trees more than
100 feet tall -- and from chewed fruit, which yielded cells from inside the
Paternity tests on the DNA yielded a shocking result: Of 13 infants, only
seven were fathered by members of the Tai Forest group.
Richard Wrangham, a Harvard professor who studies chimpanzees in Uganda,
said that because of the animals' ferocious territorial behavior,
extra-group couplings might actually have a practical benefit: A female that
has such a tryst creates the possibility that her offspring may be related
to a neighboring male. That might lead the neighboring male to show mercy
in a future encounter with her or her offspring.
In his own research, Wrangham has seen females lurking about a neighboring
group's territory. So he was not surprised to learn that some infants among
the Tai chimps have fathers from other groups.
"But even so, 50 percent seems extraordinarily high," he said. "There's
still a lot that's mysterious about this."
Gagneaux's findings, published in today's issue of the journal Nature, give
female chimpanzees a much more important role in the reproductive process.
Evolutionary biologists often treat females as a prize to be won by the most
deserving male. But Gagneaux said that's the wrong way to look at things.
"Females are not some sort of resource that just wait there like fruit to
be picked," Gagneaux said. "Females have their own agenda."
Apparently, that agenda includes sneaking off to mate with their hunkiest
neighbors. It's common in chimpanzee society for a female to disappear for
a day or two, so nobody really notices the absence of a trysting female.
But if she were to be caught, Gagneaux said, dire consequences would result.
Male chimps physically dominate females to get what they want, and sometimes
kill infants that they believe aren't theirs.
Chimp societies are complicated affairs, with strictly obeyed but constantly
shifting hierarchies that determine which animals get the best fruit, mates
and sleeping nests. Neighboring groups almost never interact, except to
fight over territory.
Since those fights are females' only opportunity to check out the neighbors,
Gagneaux hypothesizes that all the histrionics that males engage in during
the conflicts -- the hooting, the stomping, the thumping of trees -- may be
the chimpanzee equivalent of mowing the lawn shirtless.
Copyright 1997, Associated Press, All Rights Reserved
ENN Daily News -- May 22, 1997
Copyright 1997, Environmental News Network
© 1997 Peter Langston