In Experiment 1, female but not male macaques looked longer at a male scrotum on a red background compared to a male scrotum on a blue background or a seashell on either color background, or compared to the looking behavior of males. * = the interaction term [Female]*[Scrotum Red], labeled as Macaque Red on the chart, was significant. In Experiment 2, there were no significant differences in looking-time across conditions. Bars represent mean looking duration, and error bars represent 95% C.I.