Most female mammals go into some form of estrus, or heat, when fertile, displaying hormone-induced behavioral changes that mark ovulation. Scientists used to think that humans were the exception, but evidence is mounting that women may undergo their own, albeit subtler, period of heat.

A number of recent studies have shown that ovulating women appear—and even smell—more attractive to men. And a recent University of New Mexico study found that female strippers earn up to twice as much tip money during their most fertile period as compared with other times.

But Meghan P. Provost, a psychologist at Mount Saint Vincent University in Halifax, says that women in heat are not interested in just any man. Research suggests that ovulating women favor men who have more masculine qualities, such as a strong jawline. And Provost recently published work showing that women’s walks appeared sexier to men when they were not in the fertile phase of their cycle. Provost says that one explanation for this surprising result is that the attractive cues women give off when fertile are intended for people they choose to interact with, whereas walking is more public.

Psychologist Geoffrey Miller, who led the New Mexico study, notes that this pickiness does not make us so different from our caterwauling primate relatives. “It’s a common misconception that females are always promiscuous during heat,” Miller says. “In most species females are being very choosy.”

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