Human's ability to form long-term cooperative relationships between unrelated individuals is one of the main reasons for human's extraordinary biological success, reveal researchers.
The hormone oxytocin plays a role in it. Researchers of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, measured the urinary oxytocin levels in wild chimpanzees after food sharing and found them to be elevated in both donor and receiver compared to social feeding events without sharing.
Furthermore, oxytocin levels were higher after food sharing than after grooming, another cooperative behaviour, suggesting that food sharing might play a more important role in promoting social bonding.
By using the same neurobiological mechanisms, which evolved within the context of building and strengthening the mother-offspring bond during lactation, food sharing might even act as a trigger for cooperative relationships in related and unrelated adult chimpanzees.
In chimpanzees, for instance, increased urinary oxytocin levels are linked to grooming between bonding partners, whether or not they are genetically related to each other.
To examine the ways in which oxytocin is associated with food sharing, Roman Wittig and colleagues of the Max Planck Institute for Evolutionary Anthropology in Leipzig have collected and analyzed 79 urine samples from 26 wild chimpanzees from Budongo Forest in Uganda within one hour after the chimpanzees either shared food or socially fed without sharing.
The result: A chimpanzee's urine contained significantly higher levels of oxytocin after sharing food with another group member than just after feeding socially regardless whether the animal was the donor or the receiver of the food.