A woman's relationship satisfaction changes as she nears ovulation, when she's most fertile. But whether or not she's more or less happy with her guy depends on his sex appeal.
Jealousy and mate guarding — actions that men perform more frequently when their partners are fertile, according to research — may have coevolved to counter cheating. Larson’s lab previously showed that men identified as not very sexy were more jealous and attentive to their mates on the women's high-fertility days.
In the future, Larson plans to study whether or not women actually change their behavior — treating less desirable partners differently than sexier guys, or even cheating on them — when fertile.