A researcher called Martha McClintock studied the menstrual cycles of 135 women in an American college.
McClintock went to Berlin, But returned to Cornell the following year.
Dr McClintock hypothesised that this was because the women who were spending time together had the chance for their pheromones to affect each other.
But at the State University of New York, two evolutionary psychologists were puzzled to discover that lesbians show no McClintock effect.
"[McClintock] found that the onset of the date of menstruation was more similar among friends and roommates than among random pairings of women," says Alvergne.
