Rape as an Adaptation ?
Source:
owner-end-violence(AT)edc-cit.org
From : Anne Conners [ anneconners(AT)earthlink.net ]
Here is a critique of Thornhill and Palmer's "A Natural History of
Rape" that ran in Nature, Vol. 404, on March 9, 2000. Nature, published in London, is the pre-eminent journal of
record for the international scientific community.
This review is copyrighted. It
is cleared for online distribution by permission of the authors.
A theory that rape has its origin in evolutionary biology is seriously
flawed.
By Jerry A. Coyne and Andrew Berry
Jerry
A. Coyne is in the Department of Ecology and Evolution, The University of
Chicago, 1101 East 57 Street, Chicago, Illinois 60637, USA.
Andrew Berry is at the Museum of Comparative Zoology Labs, Harvard University,
26 Oxford St, Cambridge MA 02138 USA
In A Natural History of Rape, Randy Thornhill and Craig Palmer argue that rape
is an adaptation - that it has evolved to increase the reproductive success of
men who would otherwise have little sexual access to women. Their analysis of
rape then forms the basis of a protracted sales pitch for evolutionary
psychology, the latest incarnation of sociobiology: not only do the authors
believe that this should be the explanatory model of choice in the human
behavioural sciences, but they also want to see its insights incorporated into
social policy. Thus, in a single
slim volume, Thornhill and Palmer give us both an inflammatory analysis of a
sensitive topic, and a manifesto outlining evolutionary biology's future
conquest of the social sciences.
In the furore that has greeted the book's publication, the scientific evidence
for the authors' arguments has been largely ignored. However, it is here that we
must start. If their specific
claims about rape are not scientifically sound, then the authors' grand vision
of the centrality of natural selection to every aspect of our behaviour
collapses as well. In their media appearances, Thornhill and Palmer cloak
themselves in the authority of science, implying that the controversy over their
ideas is purely political, and that the underlying biology is unimpeachable.
This is a serious misrepresentation.
What persuasiveness the book does possess rests on an ingenious rhetorical
trick. The authors lay out two
alternative evolutionary hypotheses: rape is either a "specific
adaptation" (i.e., natural
selection explicitly promoted the act) or a "by-product of evolution"
(i.e., there was no direct selection for rape; rather it is an accidental
product of selection for, say, male promiscuity and aggression). Readers unconvinced by the specific-adaptation argument
therefore find themselves embracing by default the by-product alternative.
Either way, Thornhill and Palmer claim a convert.
But what, in behavioural terms, is an evolutionary by-product? Everything that
is not a specific adaptation. Thus
playing the piano - an activity unlikely to have been instrumental in the
evolution of the brain - is an evolutionary by-product, because it depends on a
brain that was itself produced by natural selection. If every human behaviour can be seen as a by-product of
evolution, then the by-product idea is useless, for a theory that explains
everything is merely a truism. The
claims that rape and playing the piano are by-products of evolution are claims
without content.
It is not surprising, then, that A Natural History of Rape is a largely an
argument for the specific-adaptation theory.
Thornhill and Palmer's evidence, however, either
1) fails to support their case, 2) is presented in a misleading and/or
biased way, or 3) equally supports alternative explanations. Here is one example
of each of these problems:
First, Thornhill and Palmer make much of the claim that rape victims tend to be
in their prime reproductive years, suggesting that reproduction is indeed a
central part of the rapist's agenda. But
the data they present contradicts this claim.
In a 1992 survey that attempted to deal with the substantial statistical
problem of unreported rape, 29% of U.S. rape victims were under the age of 11.
As that age group comprises approximately 15% of the female population,
under-11s were over-represented among rape victims by a factor of two.
So invested are the authors in their specific-adaptation hypothesis that
they try to explain this nonadaptive anomaly by noting that the data do not
indicate the "proportion of the victims under 11 who were exhibiting
secondary sexual traits."[p.72] Further, "the increasingly early age
of menarche in Western females contributes to the enhanced sexual attractiveness
of some females under 12." [p.72]. In
the end, the hopelessness of this special pleading merely draws attention to the
failure of the data to support the authors' hypothesis.
Second, Thornhill and Palmer contend that, based on sociological studies, female
rape victims of reproductive age are more traumatized by the experience than are
women either too old or too young to reproduce.
The rationale is that reproductive-age women are in effect mourning the
lost opportunity for mate choice which rape, in the worldview of evolutionary
psychology, represents to them. The authors see this apparent heterogeneity in the reaction
to rape as supporting their claims about the reproductive essence of the act.
In checking the cited reference (one of whose authors was Thornhill himself), we
find that the original work's conclusions differ critically from those given in
the book. According to Thornhill
and Palmer, the cited study shows post-rape trauma to be higher in
reproductive-age women (12-44) than in the two other age classes (under 12 and
over 44). In fact, the data show
that the only heterogeneity in response to rape comes from the under-12 class:
the over-44 class is just as traumatized as the 12-44 one.
However, when the over-44 and under-12 classes are pooled, the under-12 effect
of less trauma makes this combined "nonreproductive" class
significantly different from the 12-44 one.
The authors have used statistical sleight of hand to buttress their
argument. And we need hardly point
out that the relative lack of trauma in the youngest age group may be unrelated
to sexual immaturity: rather, children may be less able to express their
feelings. Furthermore, the original study's data are questionable because much
of the assessment of trauma in the under-12 class was necessarily based on
reports of the child's caregivers rather than of the child herself.
Direct comparison of observer-reported and self-reported data on such a
subjective issue is extremely problematic.
Finally, the fact that women of reproductive age experience more violence during
rape than do older women or children - suggesting that they fight back harder -
is taken by Thornhill and Palmer as evidence that they have more to defend.
There is, they contend, more at stake - reproduction, no less-for
reproductive-age women. While it is
true that reproductive women who resist rape may be partly motivated by the fear
of unwanted conception, it is also true that such women, at the peak of bodily
strength, are most physically capable of fighting back. Children cannot fight
off a full-grown man, and older women may also find resistance beyond them. In
exclusively championing their preferred explanation of a phenomenon, even when
it is less plausible than alternatives, the authors reveal their true colours.
A Natural History of Rape is advocacy, not science.
We have highlighted just three examples of the book's flawed arguments. There
are many more. The evidence that
rape is a specific adaptation is weak at best.
In keeping with the traditions established early in the evolution of
sociobiology, Thornhill and Palmer's evidence comes down to a series of
untestable "just-so" stories.
Sociobiological approaches to human behaviour may yield interesting insights.
But it is disciplinary hubris - a longstanding feature of evolutionary
psychology- to suppose that natural selection underlies our every action.
Because of the central role of reproduction in Darwin's theory, sexual behaviour
is in principle a good candidate for fruitful sociobiological study, but even
here it usually fails dismally. The most imaginative and committed
sociobiologist would be hard pressed to show that masturbation, sadomasochism,
bestiality, and pornography's enthusiasm for high heels are all direct
adaptations. In its insistence on forcing everything into the straitjacket of
adaptation, evolutionary psychology offers a woefully incomplete perspective on
human behaviour. Thornhill and
Palmer have inadvertently revealed just how deficient that perspective is.
Jerry A. Coyne is in the Department of Ecology and Evolution, The University of
Chicago, 1101 East 57 Street, Chicago, Illinois 60637, USA.
Andrew Berry is at the Museum of Comparative Zoology Labs, Harvard University,
26 Oxford St, Cambridge MA 02138 USA
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