Oxytocin Encourages Group Cooperation and Coordination in Wild Chimpanzee Societies

A team of researchers has found that the hormone oxytocin is released during conflicts between chimpanzee groups. The findings will help researchers better understand both human and chimpanzee warfare. The details were just published in the journal Proceedings of the National Academy of Sciences.

Warfare involves complex cooperative behaviors that are typically only seen in humans and their wild chimpanzee relatives. Chimpanzees will band together to aggressively defend their group from rivals and have even been known to take part in violent preemptive strikes. By studying war in chimpanzee societies, researchers can gain insights into the evolution of human warfare.

Scientists from the Max Planck Institute for Evolutionary Anthropology studied the role of oxytocin in wild chimpanzee group conflicts. Oxytocin is often called the “love hormone” because it enhances social bonding, especially between a mother and her offspring. Past research has revealed other possible functions of the hormone, including group coordination and defense. The research team investigated cooperative group behaviors in wild chimpanzees to determine if oxytocin was involved.

The team studied wild chimpanzees in Taï National Park, a huge rainforest in West Africa. The researchers tracked 20 individuals, 10 males and 10 females. Urinary oxytocin levels were monitored throughout the study. The researchers focused on cooperative behaviors—intergroup conflicts and hunting. The team found that all of the chimpanzees had increased oxytocin concentrations right before and after these events. High levels of oxytocin improved overall group coordination. During intergroup conflicts, the hormone was a better predictor of cooperation than the risk posed by the outside group. The authors suggest that oxytocin works similarly in humans during warfare and other events that involve conflict between groups.

For the first time, researchers have been able to show that oxytocin is released during activities that require group cohesion—at least in wild chimpanzee societies. The hormone encourages group coordination and defense. Oxytocin likely plays the same role in humans and may explain certain aspects of human warfare.


Samuni et al. Oxytocin reactivity during intergroup conflict in wild chimpanzees. Proceedings of the National Academy of Sciences (2016).

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