When women approach their most fertile time of the month, they tend to prefer potential sexual partners with more outward signs of genetic fitness, such as facial symmetry, according to past research. Now scientists find that women behave differently toward strangers in a nonsexual context, too. A paper in the April Biological Psychology showed that women near ovulation were less willing to trust strangers in an investment game, especially if the strangers were male and even more so if they were attractive men. Higher levels of the hormone estradiol, which peaks just before ovulation, were associated with less trust—a sign that the women's heightened wariness has roots in the physiology of the menstrual cycle. The finding supports the idea that at ovulation, women may unconsciously temper their increased attraction to masculine men by interacting with them more cautiously.