Cutting the competition
Mutilating male members may mar men's mischievous matingsThe Economist
19 June 2008
By Kurt Kleiner
and other forms of male-genital mutilation are commonplace in many
societies around the world. The origin of these practices, however,
puzzles anthropologists and evolutionary biologists. They wonder what
benefit they could bring, especially given the obvious risks of
infection and reduced fertility.
Explanations have ranged from
the pragmatic (a ritual that marks the beginning of adulthood and bonds
men together) to the Freudian (having something to do with the pain of
the separation from the mother). However Christopher Wilson, a
neurobiologist at Cornell University, has a different idea. In a recent
paper in Evolution and Human Behavior he suggests that male-genital
mutilations are actually intended to prevent younger men from fathering
children with older men's wives.
Dr Wilson takes his cue from
sperm-competition theory, which suggests that males of promiscuous
primate species have evolved features that maximise their own sperm's
chances of fertilising an egg they might have to compete for. These
features include large testicles which produce more sperm, and
morphologically complex penises. Males of monogamous primate species,
on the other hand, have smaller testicles and simpler penises. Human
genitals are somewhere in between, perhaps reflecting the fact that
people generally form pair bonds, but are susceptible to occasional
bouts of promiscuity.
Some forms of genital mutilation have
obvious effects on fertility. For instance, several African and
Micronesian societies practice testicular ablation -- the crushing or
cutting off of one testicle. Some Australian aborigines engage in
subincision, which exposes part of the urethra and thus causes sperm to
leak out of the base of the penis. Circumcision does not have quite
such clear-cut effects. But there are several ways it may affect
fertility: most obviously, the lack of a foreskin could make insertion,
ejaculation or both take longer. Perhaps long enough that an illicit
quickie will not always reach fruition.
Older men are in a
position to form alliances with younger men -- passing on knowledge,
lending them political support and giving them access to weapons. By
insisting that the young undergo genital mutilation of some form as a
quid pro quo, an older married man can seek to ensure that even if he
is cuckolded, he will still be the father of his wives' children. Of
course, the older man has probably undergone genital mutilation too,
and seen his own fertility reduced. But that, if anything, increases
his incentive to make certain that the young bucks are similarly
handicapped. And if all the older men in a society conclude this is a
good thing, it will rapidly become a socially enforced norm.
test this theory, Dr Wilson made several predictions. Among them, he
suggested that mutilation is more likely to be practised in polygynous
societies (since a man with several wives is more vulnerable to
cuckoldry), and is especially likely in those polygynous societies
where a man's co-wives live in separate households from their husband.
It should also take place in a public ceremony watched by other men, to
avoid cheating or free-riding. And there should be a strong stigma
against men who refuse it.
To test his predictions, Dr Wilson
looked at a database of 186 pre-industrial societies. Some 48% of the
highly polygynous ones practised a form of male-genital mutilation, and
the number rose to 63% when co-wives kept separate households. By
contrast, only 14% of monogamous societies practised mutilation.
Moreover, and also as predicted, the mutilations were almost always
carried out in public, often as part of a coming-of-age ceremony at
puberty, with strong stigma attached to unmutilated men.
Wilson's paper does not definitely prove that sexual competition is at
the root of male-genital mutilation. But it does provide a plausible
explanation for a puzzling practice. It is not likely, however, to have
much effect on attitudes toward circumcision. The men who enforce and
undergo the rituals are no more aware of the underlying evolutionary
motivations than of why their testicles are the size they are. Those
who engage in the practice for religious reasons will surely continue
to do so. Otherwise, most of the Western world has already largely
abandoned routine neonatal circumcision, which is seen as an outdated
and unfortunate medical fad.
The exceptions are America, where
more than half of newborn boys are still circumcised, and Africa, where
circumcision helps to stop the transmission of HIV, the AIDS-causing
virus. There, infection really is a far greater threat to the number of
children a man might have than the loss of his foreskin.