Smell of fertility.

It’s fairly well known that men react slightly differently to women when the women are ovulating. What the New York Times reveals is that men in relationships are less attracted to fertile women:

It’s possible that some of the men in Florida were just trying to look virtuous by downgrading the woman’s attractiveness, the way a husband will instantly dismiss any woman pointed out by his wife. (That Victoria’s Secret model? Ugh! A skeleton with silicone.) But Jon Maner, a co-author of the study, says that’s unlikely because the men filled out their answers in private and didn’t expect the ratings to be seen by anyone except the researchers.

“It seems the men were truly trying to ward off any temptation they felt toward the ovulating woman,” said Dr. Maner, who did the work with Saul Miller, a fellow psychologist at Florida State. “They were trying to convince themselves that she was undesirable. I suspect some men really came to believe what they said. Others might still have felt the undercurrent of their forbidden desire, but I bet just voicing their lack of attraction helped them suppress it.”

It may seem hard to believe that men could distinguish a woman who’s at peak fertility simply by sitting next to her for a few minutes. Scientists long assumed that ovulation in humans was concealed from both sexes.

But recent studies have found large changes in cues and behavior when a woman is at this stage of peak fertility. Lap dancers get much higher tips (unless they’re taking birth-control pills that suppress ovulation, in which case their tips remain lower). The pitch of a woman’s voice rises. Men rate her body odor as more attractive and respond with higher levels of testosterone.

“The fascinating thing about this time is that it flies under the radar of consciousness,” says Martie Haselton, a psychologist at U.C.L.A. “Women and men are affected by ovulation, but we don’t have any idea that it is what is driving these substantial changes in our behavior. It makes it clear that we’re much more like other mammals than we thought.”