Gay the gorilla and the secrets of gender

Thomas Sambrook asks what gay sex in animals teaches us humans.

Sex sells. Equal opportunities have done little to dampen the average man's (or woman's) fascination with the differences between the sexes and this, with the rising palatability of popular science, has brought to prominence a school of evolutionary psychologists who claim that, yes, men and women, boys and girls, are fundamentally different. We are stamped with our sex at birth, they say, not merely shunted down one of two arbitrary channels by a sexist society. The simplicity of the message and the eloquence with which it is stated leave us comforted with the thought that scientists have merely proved what folk knew all along. Lesley Rogers, however, is out to spoil the party.

Eschewing the bland content-free declamations that social scientists are prone to directing at biological accounts of human development, Rogers (herself a neuroscientist and behavioural scientist) critically examines, in Sexing the Brain , the dogma of the biology of sex differences. The causal chain on which such studies are pinned is as follows. An individual's genetic sex is determined by the presence of two X chromosomes (female) or by an X and a Y (male). These determine which hormones are produced, which, in turn, differentially determine all aspects of development, including that of the brain and, consequently, behaviour. But hormones, claims Rogers, are not merely a one-way conduit for the expression of genes, but a highly complex system in their own right, acting at the "interface of nature and nurture". While genetic make-up is fixed, its expression is controlled, in part, by hormones that are themselves affected by environmental factors. The causal chain linking genes and behaviour can thus be reversed. Furthermore, while hormones show a powerful and unvarying effect on the development of gonads, these organs are simple, while the brain is complex and so shows a complex response to hormonal input. This is all the more so with the human brain than with any of the simpler animals on which hormonal studies of sex differences are often based.

Rogers does a good job of exposing the chinks in reductive explanation. She astutely observes that science tends to intercept processes of change at a single point in time, leaving us able only to speculate on causes, at which point we fall back on ideology. Reductive explanations reflect conservative values and forces. Whether they constitute "an effort to recruit science into the social debate and uphold the status quo" is more questionable, however. Whose effort exactly? Sociobiologists commit the naturalistic fallacy (what is, is what ought to be) less often than it is convenient for their detractors to suppose. Rogers's charge is effectively the reverse: she accuses reductionists of asserting that what ought to be (from the sexist point of view) is what is.

The reason why we should take seriously the primacy of the environment in gender differences is not that reductive explanations are intrinsically flawed, but because they are much easier to come up with than those that embrace the potential complexity of nature-nurture interactions, not least because their proponents do not need to be trained in everything from genetics to social psychology. I suspect that a preference for reductionism does not reflect politics, but expediency of communicating hypotheses and explaining results, and thereby getting grant money and publication space. This is a serious source of bias, and Rogers's book will, I hope, stand as a corrective mechanism. The truth of Rogers's bold assertion that "the future of our sex differences belongs to us" yet remains to be demonstrated.

Ideology's impact on science is central to Bruce Bagemihl's magnum opus on animal homosexuality, Biological Exuberance . Although I have gone on to observe it myself, as a PhD student I flatly denied the possibility of non-reproductive sexuality in animals until a colleague showed me a photograph he had taken of oral sex in macaques. Even then I wondered if it might be some clever camera trick.

Bagemihl claims that ethology has systematically failed to report, dressed up as aberrant and otherwise theoretically marginalised a century of evidence showing that homosexuality is a common behaviour in a variety of animal species. To that end he has compiled a "wondrous bestiary" of animal homosexuality. It can best be summed up by saying that they do everything we do, and, given anatomical differences, plenty that we cannot. A dolphin's blowhole is not purely for blowing bubbles nor an elephant's trunk for stealing buns. In some species, straight sex is unusual; 64 per cent of female bonobo sexual interactions are same-sex. It may be objected that this is not sex as in sexual reproduction. But when ethologists speak of sex they speak not of the fusion of gametes but of acts of courtship, intercourse, pair bonding, and such. Pairs of male black swans having acquired a clutch with the assistance of a female will have nothing more to do with her and will raise the offspring themselves, very effectively, since their greater size enables them to control a larger territory. In contrast, male macaques and orangutans, which never pair-bond, may engage in anal sex. However you define it, the fact of animal homosexuality remains.

Inevitably we must ask: what light does this shed on human sexuality? In revising how we regard the natural world, Bagemihl's book may ultimately do as much for gay and lesbian rights as have several decades of social campaigning. Animals strongly mould our perceptions of behaviour.

Yet, as Bagemihl notes, they are symbolic, their significance lying not in what they are but in what we think they are. Biological Exuberance stands to change our perceptions of nature. Whether the phenomenon itself is comparable for humans and animals is less clear. The author notes that in humans we cannot measure the act, but can ask participants how they feel about it, while the reverse holds for animals. But then one might say the same of the "phenomenon" of heterosexual couplings, where continuity between humans and animals is zealously propounded by biologists.

Animal homosexuality is important for us then, but how important is it for the animals themselves? What is its function? Dismissing sociobiological explanation, the author presents a new paradigm: biological exuberance. This is best described in the words of the author as "driven by excess as much as scarcity", such that "behavioural versatility is best regarded as a manifestation of the chaotic ordering of the world, rather than a response to it" so "biology must reconsider functional explanations based on natural selection and recognise the inherent multiplicity of all life". The author unselfconsciously slips in and out of adaptive explanations, and I am at a loss to judge biological exuberance as I am unable to understand how it works. The Darwinian principle of competitive exclusion adequately accounts for the multiplicity of life, and behavioural versatility may result from a number of known forces, including sexual selection. This splendid and thorough account of animal homosexuality does not topple Darwinism but reaffirms how complex and surprising the propagation of genes by an animal can be.

Thomas Sambrook is teaching fellow in psychology, University of Stirling.