"Cuddle Hormone" May Help Chimpanzees Wage War

Chimp preparing for war

Chimp war can be brutal, and the hormone may help allies bond. Liran Samuni

We usually think of the hormone oxytocin, known as the "cuddle hormone" or "love hormone", as being released when mothers cuddle their infants, or when lovers cuddle each other. But a new study suggests it may have another use other than bonding individuals together – preparing them for war instead. Researchers have found that as chimpanzees prepare themselves for battle, levels of oxytocin surge, suggesting that the hormone may have a more sinister function.

This is not the first time that the hormone has been implicated in aggressive situations. Previous experiments have found that humans split into teams and presented with a competitive task also show spikes in their oxytocin levels, but this latest study from the Max Planck Institute for Evolutionary Anthropology has confirmed a similar thing occurs during real conflict in apes. In the human studies, they found the hormone triggers social cooperation, bonding, and a tendency to defend fellow members of their group against those in another.


The researchers of this latest paper, published in the Proceedings of the National Academy of Sciences, studied two groups of chimpanzees living wild in the forests of the Taï National Park, Ivory Coast. Both groups, each made up of five males and five females, are habituated, allowing the researchers incredible access to the apes, including the ability to collect urine samples as soon as they have been produced.

“We found high urinary oxytocin levels in hunting and intergroup conflict,” explained Liran Samuni, the first author of the paper. “Both contexts involve group coordination. The chimpanzees’ hormone levels were significantly higher than in contexts without coordinated group activity.” 

Taking into account things such as the individual's rank within a group, or proximity to the community’s territory border, the researchers found that both males and females experienced oxytocin spikes before group activities, such as hunting and warfare.

This suggests that the hormone is doing a similar role to that which has been found in the human lab experiments. The researchers suspect that the role of oxytocin in helping members of the same community bond in the build up to war could well have evolved from the role it plays in prompting mothers to defend their offspring. It means that individuals are more likely to cooperate with each other, while at the same time physically protect their comrades.


It seems that oxytocin may be helping the chimpanzees make love and war.


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