Jealousy in Titi Monkeys

Contributed by Marielle Grenade-Willis

Psychologists define jealousy as an integrated and powerful emotion that occurs when a third party intercedes in an established relationship as an actual or perceived threat. Although the emotion can become corrosive when not handled properly in relationship, many evolutionary psychologists theorize that jealousy first evolved as an emotional mechanism to keep a bond intact. Studies of jealousy in nonhuman animals have been few and far between, but recent research on titi monkeys suggests that they may be capable of this emotion. Scientists had male titi monkeys experience two conditions: one in which their female mate was interacting with a stranger male (jealousy condition) and one in which a stranger male and stranger female were interacting (control condition). The monkey’s response showed “positive associations between the jealousy condition and plasma steroid hormone concentrations of testosterone and cortisol. Testosterone concentrations were measurably higher in the jealousy condition, with a small to medium effect size.” Although the researchers cannot decisively say if the monkeys were actually feeling jealousy, the study does offer more awareness about how exactly nonhuman animals like primates form relationships to each other and if they can possibly be bitten by the “green-eyed monster”.