Male Baboons See Red as a Mating Come-Hither

Thu Mar 15 10:42:46 EST 2001

USA Today; Arlington, Va.; Mar 8, 2001

HEADLINE: Male Baboons See Red as a Mating Come-Hither

BYLINE: Tim Friend

Female baboons use their swollen red bottoms like male peacocks use their
tails to advertise their reproductive prowess and drive the opposite sex
wild with desire, new research shows.

Scientists have known for more than a century that these swellings of
perineal skin functioned as a display signal involved in mating. But whether
it indicated a female's degree of fertility or something else was unclear.
The new research conducted in Africa is apparently the first to show that
genetic fitness is the message being interpreted by males, say Leah Domb of
Harvard University, and Mark Pagel of the University of Reading,
Whiteknights, United Kingdom.

The swellings appear when females are in estrus, or ovulating. These
swellings are found in females of most species of Old World great apes and
monkeys -- those from Africa and Asia -- but not New World species found in
Central and South America, the researchers say.

Victorian-era people covered up the primates' swollen bottoms at zoos to
prevent their own embarrassment. But as far as male baboons are concerned,
the bigger and redder, the better they like them and are willing to fight
for them, the research shows. Observations made of olive baboons at Gombe
National Park in Tanzania found that females with larger swellings reached
sexual maturity at earlier ages, gave birth to more offspring and produced
offspring with the best chances of survival. Males fought each other more
often for access to the big-bottomed females than for females with less
pronounced swellings, the study shows. The results are published in today's

Generally speaking, the sexual swelling of female non-human primates is an
oddity in nature. It is more common among many mammals and birds for males
to display during courtship and for females to do the choosing. The displays
are usually physical characteristics that have become exaggerated over long
periods of time, such as horns or colorful feathers, or elaborate songs.

The classic example of this is the male peacock's tail, which has become
exaggerated and unwieldy over time because of preferences for larger and
more colorful tails by female peacocks. Males with the biggest tails are the
first picks of peacock ladies.

The tails honestly reflect a male's fitness because of their handicapping
potential. Males that can carry these ridiculous and useless trains of
feathers behind them must be strong, from the female's perspective.

Domb and Pagel say the sexual swelling of female baboons also appears to be
an "honest" signal like that of the peacock train, because bigger, redder
bottoms accurately reflect fitness in females.

However, to meet the definition of an honest signal, the signal must be
costly to produce, such as the peacock's tail. How costly the swellings are
to females is open for debate, experts say.

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