The females of many species of primates show differences in their physical appearance during their fertile period to attract the males. Until recently it was thought that human ovulation, or the fertile part of the menstrual cycle, was not visually manifested in any way. According to a study recently carried out by Czech and British scientists, it might not be quite so.
The head of the Czech team, Jan Havlicek from the Faculty of Humanities of Prague's Charles University explains how the study came about.
"There are basically two reasons; before we already started research about odour attractiveness across the menstrual cycle. So that was one reason, and the second one was just anecdotal observation by the wife of my boss who came with the idea that her lips changed across the cycle. So we decided to test this idea; whether there are differences in attractiveness."
Forty-eight women between the ages of 19 and 33 volunteered as models for the study. For the purpose of the study it was essential that they were not using contraceptive pills. Two photographs were taken of each woman around the time of ovulation and then in the third week of their cycle. The models were not allowed to use make-up and they were not told why they were being photographed.
"It was based on two independent samples. One is from Newcastle and one is from the Czech Republic, from Prague. In both cases it is based on photographs of students of the Faculty of Science and the Department of Psychology in Newcastle. These standard photographs were rated by other students, males and females who were forced to choose between two pictures of one female in different parts of her cycle."
One hundred and twenty-five women between 18 and 33 years of age and the same number of men, aged 19 to 44, were asked to choose the more attractive photograph of each female. Jan Havlicek from Charles University describes the results.
"We found out that people in general, men or women, prefer or pick, statistically significantly more often, pictures taken in the follicular phase of the menstrual cycle."
So the study suggests that women are perceived as more attractive during the fertile part of their cycle. Are there any practical implications of the results of the study?
"The most important thing is there are important theoretical implications. Because there is a number of theories that are based on concealed ovulation in humans. They speculate about its role in human evolution. But we found out that ovulation in females is not as concealed as was supposed before. So it could be practically used, like a side product, for other studies which focus, for example, on human mate-guarding. For example, whether men watch their partners more closely during the time of ovulation, or if there are any changes across the cycle. So it is based on the idea that [men] can somehow detect their [partners'] fertility."