Sex has always had its fair share of complications, for biologists and lovers alike. But some of the latest research on the subject adds a startling new dimension to the proceedings. When a man ejaculates, for example, the make-up of his semen may reflect the amount of time he has spent with his partner since they last made love. If they have been apart, he may release more sperm, perhaps because he must try and allow for the possibility that she has been unfaithful. And the woman? The timing of her climaxes may influence how many of her partner’s sperm she retains inside her body after sex – an effect which could influence her reproductive fate.
These are just two of the subtle forces at work during lovemaking, according to Robin Baker and Mark Bellis of the University of Manchester. The team’s findings (to be published this autumn in Animal Behaviour) also bring new evidence to bear on ancient sexual conundrums such as the biological significance of masturbation. Their conclusions are bold and extraordinary and will be eagerly scrutinised by other biologists. Two researchers I spoke to were respectful but sceptical; another two were more positive. All felt that the new findings were intensely interesting – a fact reflected in the large audiences that gather to hear Baker and Bellis lecture at conferences. ‘I just hope that somebody else will have a go at doing the same sort of thing,’ says Baker.
The team’s research focuses on ‘sperm competition’, a phenomenon that looms large in the lives of many animals. Whenever a female animal has sex while carrying living sperm from a previous partner inside her body, the…
