Who, in a relationship, has never experienced jealousy? It is a common emotion, especially in monogamous species, but one that is difficult to study. Researchers from the California National Primate Research Center (CNPRC), in the United States, have worked with Titi monkeys and their observations offer insight into human emotions and their consequences on the body. The results are published in the journal Frontiers in Ecology and Evolution.
Titi monkeys, native to South America, are among the 3-5% of monogamous animals in the world that form a lifelong bond with their mate. Just like humans, Titi monkeys become attached to their other half, show guarding behavior and become anxious when separated from each other. When a Titi Monkey is feeling jealous, it typically arches its back, whips its tail back and forth, and is often more excited. Some of these monkeys have also been known to physically prevent their mate from interacting with another male. While Titi females exhibit jealous behaviors just like their male counterparts, they do so in a less intense manner, making males ideal for study.
Neurological and physiological changes
The researchers simulated a “condition of jealousy” in the male monkeys by separating them from their partners. The females were then placed within sight of their half with an alien male monkey. The behavior of the male faced with this situation was filmed for 30 minutes. The control condition was that the male subject saw two monkeys next to each other, male and female, that he did not know.
The monkeys exhibited hormonal changes, specifically an increase in testosterone and cortisol levels. Increased cortisol is an indication of social stress and, in this study, correlated directly with the length of time in which male monkeys observed their partners with another monkey. The increase in testosterone is associated with the desire for mating. Brain imaging, meanwhile, revealed increased activity in the cingulate cortex, a brain region 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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