Gelada

Geladas live in the most complex multi-level society known in primates. The basic unit is a 'one-male unit' (OMU) containing a leader male, several females, and their offspring. OMUs aggregate into bands of 30-200 individuals, bands into communities of up to 600, and communities into massive herds exceeding 1,000. Each level serves different social functions, creating a nested hierarchy of reciprocity networks.

Female relationships drive social structure more than male competition. Within OMUs, females are typically relatives who groom extensively and support each other against the leader male. If females collectively reject a male, he loses his reproductive position. This female coalition power constrains male despotism—leader males maintain position through female tolerance, not physical dominance over females.

Reciprocity operates at multiple scales. Within OMUs, grooming reciprocity predicts coalition support. Between OMUs within bands, males tolerate each other near females because bands cooperate against predators. Between bands, communities share grazing areas during non-breeding season. Each level has its own exchange currency: grooming within OMUs, tolerance between OMUs, territorial sharing between bands.

The vocal communication system matches social complexity. Geladas produce the most sophisticated vocal repertoire of any non-human primate, with calls encoding individual identity, emotional state, and social context. This vocal richness likely evolved to manage relationships across the vast gelada social network—you can't groom 600 individuals, but you can maintain relationships through vocal contact.

For organizations, geladas demonstrate how multi-level structures create multiple reciprocity networks. Small teams nest within departments within divisions within companies, each level with its own cooperation logic. Managing these nested networks requires different strategies at each scale.