Symmetry...the key to attraction?

The days of assuming a strategic posture to show off your better side are numbered. For not only are symmetrical women more attractive, but it now seems that they are more fertile.

Extensive research has revealed that women whose left sides are almost identical to their right sides have 30 per cent higher levels of female hormones, increasing chances of conception.

It has long been suggested that the more symmetrical a woman's facial features are, the more attractive men will find her. But the latest study goes further, claiming that the entire body's symmetry plays a key role in indicating how fertile it is.

Scientists at Harvard University claim that women whose feet, ankles, hands, fingers, eyes, breasts, arms and ears are the same size on each side have an abundance of the hormone oestradiol.

"Our results suggest that symmetry is related to higher levels of oestradiol and, thus, higher potential fertility. As a consequence, men attracted to more symmetrical women may achieve higher reproductive success," said the researchers.

To test the theory, researchers at Harvard and colleagues at European institutions carried out detailed investigations on about 200 women aged 24 to 36 with regular menstrual cycles, no fertility problems, and who were not using hormonal contraception. The researchers used measurements of the fingers on the left and right hands of the women as markers of symmetry. The second and fourth digits of each hand were measured to the nearest millimetre. If the fourth left and fourth right fingers differed in length by up to 1mm, the woman was classed as symmetrical, while those with differences greater than 2mm were asymmetrical.

Saliva samples were taken and tested for female hormones. The results show that there were considerable differences between the two groups of women. Symmetrical women had 21 per cent higher mid-cycle female hormones than asymmetrical women. At other times the differences was as high as 28 per cent.

"Oestradiol produced during the menstrual cycle is crucial for successful conception, and levels of oestradiol are important indicators of a woman's ability to conceive," said team leader Dr Grazyna Jasienska of the Radcliffe Institute for Advanced Study at Harvard University.

She added that the average hormone levels are associated with the probability of conception of 12 per cent, while a 37 per cent rise in levels increases the probability to 35 per cent.

"In our study, levels in symmetrical women were almost 30 per cent higher than those in asymmetrical women. Such difference in hormone levels suggests a substantial increase in the probability of conception for symmetrical women," they said.

They suggest that higher levels of female hormones may also explain why symmetrical women are healthier, because the hormones are known to stimulate the immune system. The downside for symmetrical women is that high levels of female hormones during the reproductive years may cause problems in the post-menopausal years because, say the authors, high levels of the hormones are linked to an increased risk of breast cancer and other malignancies.

Other research at the University of New Mexico shows that people with symmetrical faces are better able to fight infections. The common cold, asthma and flu are all more likely to be combated efficiently by those whose left side matches their right.

University of Western Australia researchers have also found a link between symmetry in men and sperm quality. They found that those with left and right side differences had poorer sperm quality. They say the finding may explain why women are unconsciously attracted to symmetrical male faces.

The secret of sexual attraction is in the smell

The secret of sexual attraction can at last be revealed - starting with that first longing look through to canoodling and, for some, consummation. And it's not so much about that certain special chemistry as it is about certain special chemicals. Far from being an intangible, poetic feeling of "connection", lust and love can be boiled down to a set of compounds - and smell.

In one of the first academic studies into the subject, reported in the medical journal Sexual and Relationship Therapy, psychiatrists set out to define sexual chemistry and list its ingredients, a feat that has eluded most researchers.

A team from the Robert Wood Johnson Medical School in New Jersey says a chemical in the central nervous system - norepinephrine - imprints images of the loved one; serotonin is responsible for intrusive thoughts about the partner; dopamine provides the exhilarating physical symptoms; and the neurotransmitter phenylethylamine stimulates falling in love.

Hormones also play a role, with vasopressin encouraging exclusive focus on one partner, and oxytocin triggering cuddling. Androgen levels are also linked to higher levels of sexual drive.

Body smell plays a big part as well. The report asserts "that sexual chemistry in humans may be influenced by the unconscious attraction by two individuals to each other's unique odour".

Roger Dobson