Who in a relationship has never felt jealousy? It is a common emotion, especially in monogamous species, but which is difficult to study. Researchers at the California National Primate Research Center (CNPRC), in the United States, have worked with Titi monkeys and their observations provide insight into human emotions and their consequences on the organism. The results appeared in the journal Frontiers in Ecology and Evolution.
The Titi monkeys, originally from South America, are part of the 3 to 5% of the monogamous animals in the world that form a lifelong bond with their partner. Much like humans, Titi monkeys become attached to their half, exhibit guarding behavior, and become anxious when separated from each other. When a Titi monkey is feeling jealous, he usually arches his back, whipping his tail back and forth and is often more aroused. It is also known that some of these monkeys physically prevent their partner from interacting with another male. While Titi females exhibit jealous behaviors, just like their male counterparts, they do so in a less intense way, however, which makes males ideal for study.
Neurological and physiological changes
The researchers faked a “condition of jealousy” in the male monkeys by separating them from their mates. The females were then placed in full view of their half with an alien male monkey. The male’s behavior in this situation was filmed for 30 minutes. The control condition consisted of the male subject seeing two monkeys next to each other, male and female, whom he did not know.
The monkeys exhibited hormonal changes, particularly increased levels of testosterone and cortisol. The increase in cortisol is an indication of social stress and, in this study, correlated directly with the length of time that male monkeys observed their partners with another monkey. The increase in testosterone is associated with the desire for mating. Brain imaging revealed increased activity in the cingulate cortex, a region of the brain associated with social exclusion in humans, and in the lateral septum linked to aggressive behavior. Jealousy is not necessarily negative, say the researchers. It is an evolutionary behavior acquired in order to preserve the relationship.
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