How jealous monkeys help us understand our emotions
Scientists have located the lair of the green-eyed monster in a part of the brain that responds to social rejection.
The discovery was made in a species of highly monogamous monkey that, like humans, succumbs to jealousy.
Coppery titi monkeys, from South America, form strong attachments very similar to human romantic relationships.
"Male titi monkeys show jealousy much like humans, and will even physically hold their partner back from interacting with a stranger male," said US lead researcher Dr Karen Bales, from the University of California.
To trace the source of jealousy, the scientists acted the part of the villain in Shakespeare's 'Othello'.
Just like the plotting Iago, who rouses Othello's suspicions of infidelity, they set out to stir up feelings of jealousy in the male monkeys. The primates were made to watch their female partner consorting with a male stranger while their behaviour was filmed.
Brain scans carried out after half-an-hour of viewing showed a spike of activity in the cingulate cortex, a region associated with "social pain" in humans.
Dr Bales said: "Increased activity in the cingulate cortex fits with the view of jealousy as social rejection."
Heightened activity was also seen in the lateral septum region, which is thought to play a role in the formation of pair bonds in primates. In addition, the jealous monkeys experienced a surge of cortisol stress hormone, and boosted testosterone.
Dr Bales said: "Understanding the neurobiology and evolution of emotions can help us understand our emotions and their consequences."
A limitation of the study, published in the journal 'Frontiers In Ecology And Evolution', was that it only looked at jealousy in males, she said.