A threat display from an olive baboon (Papio anubis) produces a submissive response from a second individual. Dominance (relative rankings of animals) is a major guiding force in many animal societies. In fact, in male olive baboons, more certain dominance hierarchies is associated with lower average levels of cortisol, a hormone that is typically associated with stress (Sapolsky & Ray, 1989). These two baboons were photographed on the beach of Lake Tanganika (the second deepest lake in the world!) at Gombe Steam National Park in Tanzania.

[Photo and caption by Alexander Vining]

Sapolsky, R. M., & Ray, J. C. (1989). Styles of dominance and their endocrine correlates among wild olive baboons (Papio anubis). American Journal of Primatology, 18, 1-13.