Sex is best when you lose your head

Review by James Meek

• Promiscuity: An Evolutionary History of Sperm Competition and Sexual Conflict by Tim Birkhead
  
  Faber, 272 pp, £9.99, May 2000, ISBN 0 371 19360 5

In 1853 the Reverend Frederick Morris, an opponent of Charles Darwin’s and a man with a Victorian sense of propriety, urged his parishioners to emulate the fidelity of a small bird called the dunnock. Be thou like the dunnock, he told them – the female and the male impeccably faithful to each other.

Charles Robert Darwin. A copy made by John Collier (1850-1934) in 1883 of his 1881 portrait of Charles Darwin. According to Darwin's son Erasmus, "The picture is a replica of the one in the rooms in the Linnaean Society and was made by Collier after the original. I took some trouble about it and as a likeness it is an improvement on the original." Given to the National Portrait Gallery, London in 1896. See source website for additional information. (Photo credit: Wikipedia)

What would the Rev. Morris have made of the scandalous truth? Far from being monogamous, the dunnocks, from a Victorian point of view, have shockingly lax morals. The female dunnock often takes not one but two males as partners. The best a stern man of religion could say about dunnocks is that there’s no superfluous bump and grind when they mate – it’s strictly fertilisation business, over in 0.1 seconds. Fast enough to do it while your mother’s back is turned.

Tim Birkhead and his fellow evolutionary biologists, exploring the nature of sexuality across species from single-celled organisms to humankind, are the paparazzi of the science world. They travel to remote islands and put up with extreme discomfort in the hope of catching animals having sex with each other, and when they do, splash their names and their pictures over the pages of the science journals. It doesn’t always work out. Fiona Hunter and a colleague, later to expose what the mainstream media dubbed ‘penguin prostitution’ in the Antarctic, once watched a colony of fulmars on Fair Isle for 56 days on the trot, 18 hours a day, only to find the species relatively faithful: a mere 16 per cent of females had sex with a bird who wasn’t their partner, and there were no ‘illegitimate’ chicks. This isn’t a glamorous pursuit. Geoff Parker, one of the human heroes of Birkhead’s story, spent months with his face a few centimetres away from fresh cowpats, watching female dungflies being aggressively mounted by two males in turn. Sometimes the biologists witness scenes more disturbing than they had anticipated: Mats Olsson, observing the rape-like mating of the Lake Eyre dragon in Australia, saw a male lizard bite his female victim so hard while impregnating her that she died.

Often it is not enough to be a mere voyeur with a long lens. Like a manipulative aristocrat in a Jacobean drama, the intrepid investigator arranges things: Birkhead gets live zebra finches to mate with dead ones, Nicholas Davies and Ian Hartley make it possible for female dunnocks to take a third husband.

A Dunnock, Prunella modularis, photographed in Torquay, Devon, England in April 2008. (Photo credit: Wikipedia)

Decades of accumulated work of this kind have changed our understanding of the nature of sex, reproduction and the different roles of male and female. From Darwin’s time up to the late 1960s – not coincidentally, the time when the intellectual assault on male-centred academic thinking got under way in earnest – it was thought that male animals competed for female partners, with the strongest and most attractive impregnating the most females; that females sought only monogamy, and if they did have sex with multiple partners (and biologists couldn’t help noticing that they did) it was against their will, always a form of submission to rape.
In the past thirty years, the conventional wisdom has been destroyed. The truth is that females of most species actively seek multiple partners to have sex with. If the aim of males is to put their sperm into as many females as possible, females are trying, with equal determination, to get the very best sperm to fertilise their eggs – even if that means having sex with many males in turn.

Rivalry between males and discrimination by females extends beyond the sexual act itself. Inside the female, the sperm of different males fight for supremacy – this is sperm competition. At the same time, the female may be able to select the sperm that are best for her – this is sperm choice. This is the true battle of the sexes. The males and females of each species are permanently locked in a struggle to out-evolve each other as their reproductive equipment and behaviour change to achieve their conflicting aims – i.e. maximum fertilisation v. best fertilisation.