AVID readers of women's magazines will, no doubt, be familiar with the latest “three tips” to their “best orgasm ever”. They and their exhausted partners may, however, take comfort from the fact that a group of scientists has just found that technique is not everything. Genes, it seems, also make a big contribution to a woman's ability to reach orgasm.
The researchers in question—Kate Dunn, who works at Keele University, near Stoke, in England, and Tim Spector and Lynn Cherkas of St Thomas' Hospital in London—came to their conclusion by exploring orgasmic ability in twins. Their finding, reported this week in Biology Letters, is that between 34% and 45% of the variation between women in their ability to orgasm can be explained genetically.
A twin study assumes that the individuals in pairs of identical and non-identical twins had shared family environments when they were young, allowing the genetic basis of behavioural traits to be teased out. If identical twins (who have all their genes in common) show a greater similarity in their expression of a particular trait than do non-identical twins (who have only half their genes in common), that suggests the trait is, at least in part, the result of genetic influences. To draw their conclusions, the researchers therefore asked their twins questions about how frequently they achieved orgasm through intercourse and masturbation.
What this study does not show, of course, is what the genes that influence orgasm are actually doing. One possibility is that they control the anatomy of the G-spot, a concentration of nerves in the vagina. Another is that they control variations in the pleasure centres in a woman's brain. A third is that they regulate susceptibility to anxiety, which gets in the way of an orgasm. Or it may be all three.
Nor is it clear just what orgasm is for. A variety of theories have been proposed—from cementing pair bonds between men and women to sucking into the uterus only the sperm of those males that have given a woman the most pleasure (and thus, at the same time, provided incontrovertible evidence of their physical fitness). All these theories, however, suffer from one basic defect, according to a new book on the subject by Elisabeth Lloyd*. This is that no study has yet established a reliable link between a woman's capacity to orgasm and either her ability to reproduce or how many children she eventually bears.
Another study just published in Biology Letters, by Sarah Kilgallon and Leigh Simmons at the University of Western Australia, has, however, thrown light on a previously unexplored part of the male side of reproduction. This is the question of sperm competition.
It has been known for years that in a range of animals from insects to birds the males increase the quality and quantity of the sperm they ejaculate when those sperm are likely to find themselves in competition with sperm from another male. Dr Kilgallon and Dr Simmons show that something similar happens in humans.
In this study, men were asked to abstain from all sexual activity for at least 48 hours before giving a semen sample. The semen was taken after the 52 men in the study were shown one of two types of pornographic image. The first depicted two men and a woman, while the second showed a picture of three women. The theory was that the first image, showing both a desirable female and several competitors, would be likely to induce sperm competition. Indeed it did. Men viewing this image had a higher percentage of motile sperm in their ejaculate.
Another facet of this study was that the researchers used a survey to tease out other factors that might be influencing semen quality. Keeping a mobile phone close to the testes, they found, had a significant negative impact on sperm numbers and motility, though they do not speculate why that might be.
There are some important messages for both sexes from all this research. Women might be interested to observe that certain kinds of pornography can increase their partners' fertility. And men might like to note that mobile phones are not intended as a form of contraception. And, while some men may take heart from the news that the sexual dissatisfaction of their lovers is not necessarily their fault, there is a flip side to the findings. The fortunate 14% of women who always have an orgasm seem to do so for reasons that have more to do with luck than skill.