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Why Is the Penis Shaped Like that?

And Other Reflections on Being Human

by Jesse Bering

Humans prefer nighttime sex - cooler, dark so less danger of predators or competitors, and if female lies supine afterwards, incr chance of sperm making it to the egg.

(London Times)

As you might guess from a book with a title such as this, Jesse Bering is not a man who worries about being shocking. In fact, he delights in it. A self-described 'godless, gay, psychological scientist with a penchant for far-flung evolutionary theories', he is a relentlessly provocative columnist for Scientific American and Slate magazines, from which most of the 33 short essays in this book are drawn.

His modus operandi is to plunder the kind of recent scientific research that only just survives getting 'zapped by the electric fencing of university ethics boards', and that often gets little media airtime, because it's just too controversial. He then subjects the science to his own teasingly challenging interrogation. Be warned, though: this means the more outlandish edges of sexual biology and behaviour. It means evolutionary explanations of gyrating testicles, tales of uncle-molesting sexsomniacs and moral musings on the vexed question of whether homophobes are homosexuals. The prudish and squeamish might want to look away now.

To answer, first of all, the question of the title, it appears that human males have huge penises - between five and six inches long, on average, which, relative to our primate relatives, is quite splendid. More important, they have pronounced coronal ridges (this being the flared edge of the glans; apes' members are 'more or less all shaft'). The point of all this is that as a human penis moves in and out of a (human) vagina, it creates a vacuum-like effect - which helps remove the sperm of a competitor male. The penis, then, is not just a tool for boosting a man's own chances of insemination, but for doing down the other guy. And the point of all this, for Bering, is not ­salacious titillation but that it makes you think differently about human monogamy. If we were designed to be faithful, why would we have evolved such an instrument? 'Scientific knowledge,' he urges, 'changes perspective. And ­perspective changes everything.'

From penises we descend to ... testicles. We all know they exist to keep sperm cool, but had anyone considered that they might also exist as displays of evolutionary prowess, rather like a male peacock's feathers? Rather less beautiful, admittedly, but why else would evolution place something so precious in such a vulnerable place? The testicular cooling mechanism itself is rather wonderful, too. The cremasteric muscles in the upper inner thigh, from which the testicles hang, help regulate temperature moment by moment, by retracting and then dropping the scrotum, bringing it closer to the body, or pushing it away. (The same muscles pull the testicles up during sex, to help prevent swinging and crushing injuries). More amazingly yet, each testicle helps keep itself cool by swivelling around independently, continually presenting a fresh surface area to the air.

There's plenty more like this: pubic hair is 'furry advertising' of sexual maturity, and may help protect against sexually transmitted infections. (The recent fashion for pubic-hair removal, Bering suggests, may be linked to increases in rates of gonorrhoea and chlamydia.) Acne is a consequence of the evolutionary loss of body hair: we're still trying to lubricate the fur we've lost.

Bering's more thoughtful essays concern not biology but sexual behaviour and sexual justice. Responding to research that shows that zoophilia, the desire for animals, seemingly afflicts (or affects) 1% of adults, he concludes that words like 'pervert' and 'unnatural' have all the theoretical depth of a thimble. It is a moot point, but a typically well-turned phrase. Discussing sexsomnia, a sexual variant of sleepwalking, he notes that behaviour such as fugue-state ­masturbation, weak pelvic thrusts, or steamy pillow talk is innocuous enough. But pity the 16-year-old who sleepwalked into his aunt and uncle's bedroom and began unconsciously molesting his uncle.

In controversial areas, Bering doesn't mind who he offends, and is sometimes cavalier with the science in his pursuit of shock value, eagerly seizing on controversial studies without fully acknowledging their critics. When, for instance, he mentions the famous McClintock effect, whereby women are said to synchronise their menstrual cycles, he doesn't trouble to say that the phenomenon is widely rejected as a myth founded on anecdote and flawed methodology. His presentation of 2002 research on semen also favours the shock headline over the detail - and almost seems wilfully hostile to women. He tells us that semen doesn't just feed sperm: it carries a cocktail of mood-enhancing, depression-fighting and affection-boosting chemicals, which seem to be delivered to the receptive partner as if by penile injection. One study suggested that women having unprotected sex were actually happier. The sexual politics of that proposal, never mind the science, will make many people angry, but he skates over the problem in a couple of paragraphs before ploughing on with the speculation.

On the dangerous subject of paedophilia, he is almost reckless. He argues that attraction to adolescents is much more common than we'd like to pretend, and offers evolutionary explanations for the phenomenon. He argues that whenever society screams about some demon or another, it's probably just caught an especially alarming sight of itself in the mirror. Scientists are understandably leery of commenting on this subject, which makes Bering's efforts bold, even if you disagree with him. Consider his essay on asexuality, or the absence of desire, which is scarcely ­studied at all. An analysis of data in 2004 found that 1% of the British population described themselves as never having a sexual attraction to anyone. If you consider that roughly 3% of the population describes itself as ­homosexual, yet the topic generates a thunderous amount of debate and research, that single percentage point is remarkable.

If all that sounds controversial, you've read nothing yet. How about this finding, from 1996: gay porn stimulated erections in 80% of homophobic men, compared to 34% of non-homophobes. Or this: children who exhibit gender-atypical behaviour (tomboys and sissies, to put it baldly) are much more likely to grow up to become homosexual adults than their gender-unbending schoolmates. Or indeed this: non-religious people are significantly out-reproduced by religious people. The statistics for this last finding come from analysis of a huge Swiss poll conducted in 2000, covering people of all religious denominations. The facts supposedly stack up even when you control for factors such as cultural norms, education and class, as if whatever drives religiosity in the brain might also drive a desire to breed.

This book could fuel a score of dinner-party conversations, not just for the daring of its did-you-knows, but for its cheeky sounding of their evolutionary explanations and moral implications. It is bedevilled by the usual problem of evolutionary psychology, of course: it offers all-embracing adaptational answers where complex cultural explanations might be more ­convincing. And sometimes the moral compass needs a tap, if not a jolt. Does Bering really sympathise more when paedophile crimes are perpetrated by artists such as Oscar Wilde and Andre Gide, than when they are committed by lesser men? Or is he just winding us up? But despite its stumbles, this is more than some scientific stocking-filler: it uses science to unsettle our most embedded assumptions. It is deeply thought-provoking, then, as well as shallowly provocative.

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