Friday, September 25, 1998 Published at 11:17 GMT 12:17 UK

Sci/Tech

Infidelity ‘is natural’

Females ‘stray to gather the best possible genes for their
offspring’

Infidelity may be natural according to studies that show nine out of
10 mamals and birds that mate for life are unfaithful.

Experts found animals that fool around are only following the urges
of biology.

New studies using genetic testing techniques show that even the most
apparently devoted of partners often go in search of the sexual company
of strangers.

Females stray to gather the best possible genes for their offspring,
while males are driven to father as many and as often as possible.

“True monogamy actually is rare,” said Stephen T Emlen, an expert on
evolutionary behaviour at Cornell University.

According to him, there are two kinds of monogamy – social and
genetic.

In the first kind partners bond and work together to raise their
young. With “genetic monogamy,” parents are faithful sex partners.

While social monogamy is relatively common, genetic monogamy is the
exception rather than the rule.

Dr Emlen said there are only two monkeys, the marmoset and the
tamarin, are truly monogamous.

All other primates, includes humans, often mate outside their
partnerships.

“One of the patterns is that females seek males of high status and
high quality,” said Dr Emlen.

“By doing so, they are able to produce offspring of higher quality
that will be able to do better and survive better.”

Males are said to be biologically driven to stray by the desire to
spread their genes into as many members of the next generation as
possible.

But the reasons why people have sex outside a relationship are far
more complex.

Researchers generally believe that monogamy originated among species
whose young survived best when raised by a bonded pair.

This may have led to the rise of monogamy among people, since human
children take so long to mature.

Birds of a feather

Faithful sex partnership has been thought for years to be widespread
among birds.

The eastern bluebird was considered a prime example, with male and
female partners working together to build nests, incubate eggs, then
feed and raise their young.

But researchers have found that the bluebirds have a sex life that
rivals a television soap opera.

Patricia Adair Gowarty, a behavioural ecologist at the University of
Georgia, has found that 15% to 20% of chicks cared for by a pair of
bluebirds were not fathered by the male.

She found that only 10% of 180 socially monogamous species are
sexually faithful.

The research is published in the journal Science.