The elaborate courtship displays found in the animal kingdom—a peacock spreading his feathers, the hissing of the Madagascar cockroach—aren’t always appropriate in an office or classroom. Male humans seem to have devised other, less obvious ways of showing off. A new study suggests that when young men interact with a woman who is in the fertile period of her menstrual cycle, they pick up on subtle changes in her skin tone, voice, and scent—usually subconsciously—and respond by changing their speech patterns. Specifically, they become less likely to mimic the woman’s sentence structure. According to the researchers, this unintentional shift in language may serve to telegraph the man’s creativity and nonconformity—qualities that are believed to attract potential mates. “At least a part of the interpersonal dynamic that exists when men and women are getting to know prospective romantic partners is being governed by the biology of a woman’s body and men’s sensitivity to these biological factors,” says Michael Kaschak, PhD, the senior author of the study and an associate professor of psychology at Florida State University, in Tallahassee. This idea isn’t new to evolutionary psychologists, who have long known that males of various species will change their behavior if they’re trying to find, or hold on to, a mate. In humans, these displays can include risk taking (rashly choosing to “hit” in blackjack, say), writing a romantic poem, or using big words. Moreover, previous research has found that female fertility cues tend to trigger this type of behavior in men. With that knowledge in mind, Kaschak and his coauthor designed a pair of experiments to test whether a woman’s fertility affects male speech. Their findings appear in the journal PLoS One. The first experiment included 123 male and five female college students, all of them heterosexual. The researchers tracked each woman’s fertility by marking the beginning and end of her menstrual cycle. At various points in the cycle, they paired off a woman with one of the men in a laboratory.