A SINGLE act of rape may be more than twice as likely to make a woman
pregnant as a single act of consensual sex.
That statistic will reopen the hotly contested debate over whether rape can
be a successful reproductive strategy in evolutionary terms. It could help to
explain why men raping women has been so common throughout history and across
cultures, two American researchers told the conference.
Previous studies found that rates of pregnancy resulting from rape could be
anything up to 30 per cent, compared to a 2 to 4 per cent chance of getting
pregnant from a single act of consensual sex. This led some biologists, notably
Randy Thornhill from the University of New Mexico at Albuquerque, to parade the
figures as evidence that rape is a natural way for men to spread their genes
(快猫短视频, 19 February 2000, p 44).
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But in the ensuing controversy, the studies were all roundly criticised. Some
rely on crime statistics, which may skew the figures: rape victims who become
pregnant may be more likely to report the crime than those who do not. Others
fail to measure the influence of contraception鈥攅ither preventive or
post-coital, such as the morning after pill. And some include acts of oral and
anal rape, which cannot result in pregnancy.
Jon Gottschall, a researcher at St Lawrence University in Canton, New York,
says the studies failed to answer the crucial question: 鈥淲hat is the
evolutionary success of rapists?鈥�
To find out, he and his wife Tiffany Gottschall examined the results of
National Violence against Women Survey, a study by the National Institute of
Justice and the Centers for Disease Control and Prevention. The women studied
were phoned at random and interviewed about their experiences. The Gottschalls
focused on 405 women who had suffered a single incidence of penile-vaginal rape
at some point between the ages of 12 and 45. Of these, 6.4 per cent became
pregnant. But that figure jumped to nearly 8 per cent when the researchers
allowed for the women who鈥檇 been using birth control鈥擴S government
statistics show that 1 in 5 of the women in the sample were likely to have been
using the pill or an IUD.
To complete the comparison, the Gottschalls needed to know how many women in
that age group get pregnant from one-night stands and other one-off acts of
consensual sex. The answer鈥攔eported this year in a separate study by Allen
Wilcox, head of the epidemiology branch of the National Institute of
Environmental Health Sciences鈥攚as a mere 3.1 per cent. 鈥淚t was surprising
to see this margin of difference,鈥� says Jon Gottschall.
Crucially, he believes the difference cannot be explained away by the
argument that women having regular consensual sex are, on average, more likely
to be using contraception than rape victims. 鈥淎ll the women in Wilcox鈥檚 study
were trying to get pregnant, and not taking precautions,鈥� he says. A more likely
interpretation, say the Gottschalls, is that rape really does result in more
pregnancies.
One possibility is that women feel more attractive and sexy when ovulating,
and unconsciously give off signals that rapists might pick up鈥攁lthough
it鈥檚 unclear whether men do in fact notice these signals
(see p 12). Another,
more likely explanation is that rapists target attractive and healthy-looking
women鈥攂oth characteristics that can indicate fertility. But whatever the
reason, say the researchers, none of this absolves the rapist or means the
victim is in some way to blame.
However, sociologist Frank Furedi of the University of Kent at Canterbury
says that trying to answer questions about the reproductive success of rape is
essentially meaningless. He believes that what constitutes rape or a consensual
sexual act within a relationship can be extremely ambiguous and says that phone
surveys often push women into claiming they have been raped. 鈥淲hen relationships
sour, women often redefine them in a destructive form,鈥� adds Furedi. Rape has
also meant different things through history. 鈥淐onsidering it as a strategy is
essentially nonsense.鈥� Gottschall says women may also sometimes reinterpret a
rape as a consensual act years later when the relationship has improved. He
agrees that the data in the surveys is not perfect, 鈥渂ut the best information we
have still all points in one direction鈥�.
One other question remains unanswered. For this form of rape to be a
successful evolutionary strategy, the benefits of the crime have to outweigh the
costs for the rapist. And the costs are extremely hard to judge. However, some
surveys suggest that less than 1 per cent of rapists are convicted in the US,
says Jon Gottschall. Even in traditional societies, a high proportion of rapists
may have never been punished because of the costs to the victim of reporting the
crime.
