An international team of researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, conducted behavioral observations and collected urine samples for cortisol analysis of male chimpanzees of the Taï National Park, Ivory Coast, during periods of intense male-male competition. They showed that all males had higher stress levels during periods of increased male-male competition while aggression rates were actually lower during this time.  This may indicate that in times of social instability animals refrain from aggressive actions to avoid escalation of conflicts and to promote group cohesion.