It is not only animals that rely on physical cues to gauge the fertility of potential rivals for a mate, an unusual study asserted recently. Without knowing it, human women seem to be able to recognise others in the most fertile phase of their menstrual cycle, around ovulation, simply by looking at their faces, it said. And intriguingly, this ability was pronounced in women with high levels of oestradiol, a female sex hormone linked to high general fertility.
The findings implied that more fertile women, who are likely to have more children in their lifetime, "are better at guarding their mate from potential adultery," said study co-author Janek Lobmaier of the University of Bern. The paper was published in the Royal Society Journal Biology Letters.
Few studies, if any, have tested whether women too can discern such cyclical facial differences. Lobmaier and a team showed pairs of photographs of women -- one taken in the most fertile and one in the least fertile phase of their menstrual cycle -- to over 200 other women, some in an online survey and others in the lab.
Unlike men, women did not find the faces in the portraits more or less attractive depending on when they were photographed, the team found. Overall, they also did not suspect either version to be more likely to "entice your date away from you", as the question was phrased. But looking at a subgroup of respondents for whom the team had data on naturally-occurring hormone levels, the team found an interesting trend. Those who were not ovulating but had high oestradiol levels were more likely to pick the photo of an ovulatory woman as a potential date thief. The study did not test the potential influence of naturally fluctuating oestradiol levels.
Many animals send conspicuous signals to indicate fertility -- using plumage, colouring, scent or a special call. In human, the changes are not obvious. The women in the study were not told its purpose. AFP
