Bar the doors and break out the chastity belts, boys,
because girls of most species sleep around, and it's for their own good, if
not yours.
For generations, biologists had assumed females to be
naturally chaste, while males were renowned for their promiscuity. Even Charles
Darwin, who invented the idea of sexual selection, didn't dare challenge
the Victorian morals of his day. Man evolved from ape, fine. But an immodest
and lustful Mother Nature?
Heaven forbid!
Now, hundreds of studies and a spate of books are
challenging that conventional wisdom. Females of many species, it turns out,
have evolved strategies for passing on their genes that involve copulating with
multiple males -- and recognition of that fact is literally changing our view
of the birds and the bees.
"Natural selection, it seems, often smiles on
strumpets," says evolutionary biologist Olivia
Judson, author of "Dr. Tatiana's Sex Advice to All Creation," the
most recent and entertaining book exploring the variety of female harlotry.
"As a rule, loose females have more and
healthier children."
To be sure, biologists are examining these questions in the
dispassionate light of scientific inquiry. In describing their theories, they
prefer the more neutral term "polyandry," meaning many males, instead
of "promiscuity." And they caution laypeople not to look to nature's
own apparent infidelities for any justification of their own behavior.
The misbegotten idea that males evolved to make love and
females to demur gained scientific currency in the late 1940s in fruit fly
experiments by Angus
Bateman, a British scientist who reached his erroneous conclusions in part
because his experiments lasted only three or four days.
Had he run his experiments longer, he might have discovered
that male black- bellied fruit flies secrete an anti-aphrodisiac in their semen
that's relatively short lived. As soon as it runs out, females become
interested in copulating again.
On the surface, the conventional view made sense. Sperm
seemed to come cheap to males, while eggs were expensive to females, which have
to invest the time to raise offspring. Scientists could not fathom any possible
benefit of multiple partners of females, and they could come up with plenty of
potential costs, such as sexually transmitted diseases.
BIRDS DO IT
Then came DNA paternity testing. In one species after
another, it turned out that biologists were as cuckolded as the males they had
been observing. The first and most extensive examples of polyandry were found
among avian species, which was quite a shock to scientists because birds had
appeared to be paragons of traditional family values.
"The way the male and female rush back and forth to
their demanding brood of chicks seems like nature's model of good
parenting," says Marlene
Zuk, biology professor at UC
Riverside and author of "Sexual Selections: What We Can and Can't
Learn About Sex From Animals."
"Now, we find that they're actually in the same
situation as millions of modern-day husbands and wives, eyeing a child warily
and making uneasy jokes about the milkman," she says.
DNA testing in chicks of seemingly monogamous females showed
a wide range of extra mates. In one study, for example, as much as 90 percent
of the offspring of the brilliantly colored Australian fairy wren were from
mates other than the presumed father.
Biologists have struggled to come up with broad theories for
why females benefit from playing the field, but so far the reasons seem to vary
widely according to species. A lot of complex theory boils down to this: A
gal's got to do what's necessary to ensure the survival of her genes.
Carol Cruzan Morton, Special to The Chronicle,