1Anthropology, UC Santa Barbara, 2Anthropology, University of New Mexico
March 26, 2015 9:15, Grand Ballroom E/F/G
While ultimate explanations of cooperation such as kin selection or reciprocal altruism are well studied, we are only beginning to understand the underlying proximate mechanisms. Here we focus on the roles of oxytocin, testosterone and cortisol in motivating cooperation. Oxytocin is best known for its role in mother-infant and pair bonds across mammals, but recent studies have shown that oxytocin was associated with cooperative behavior across diverse relationships including non-kin cooperation partners. Importantly, oxytocin levels during social interactions track relationship quality and may thus function as a score-keeping mechanism and to motivate cooperation with valued partners. As such, oxytocin could be responsible for overcoming the fight-or-flight and stress responses triggered by testosterone and cortisol and thereby enable cooperation, especially when stakes are high. In order to test this hypothesis, we measured salivary hormone levels collected from 31 Tsimane men during hunting and food provisioning, an ancient form of high-stakes cooperation in our species. Oxytocin showed a significant increase when hunters returned home compared to baseline (W=20, P<0.01), with changes in oxytocin levels closely tracking testosterone and cortisol levels. The amount of meat brought home (Beta=0.65) and a hunter’s number of children (Beta=0.27) had positive effects on oxytocin change, controlling for age, bmi, polygyny, testosterone change, and whether the hunter was satisfied with the hunt. These findings tentatively support the hypothesis that oxytocin interacts with testosterone and cortisol to facilitate high-stakes cooperation. We discuss our results in light of existing theory and highlight future directions.