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Department of Evolutionary Anthropology

Cooperation in Male Dolphins

Complex social relationships are thought to have been the major selective force favoring the evolution of large brains and enhanced cognition. Humans have the largest relative brain size and are considered to have no match among other species in the realm of social abilities. However, the largest brain/body size ratio outside of humans are found in dolphins whose social lives are relatively unexplored.

The social complexity hypothesis predicts that we should find complex social relationships among delphinids. This prediction appears to be borne out in a population of Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia. Here we find a hierarchical alliance system that appears to be more similar to the nested system of human male alliances than to alliances in non-human primates. If this comparison is upheld we have an extraordinary case of convergence that will be of great interdisciplinary interest.

However, gaps in our understanding of both proximate and ultimate causes of alliance formation in dolphins limit our ability investigate the comparison further. We require information on the evolutionary and ecological factors that shape dolphin alliance tactics as well as how dolphin alliance relationships are maintained and contested via social interactions and communication - topics that have been well studied in primate societies. We are in a unique position to address these deficiencies in the dolphin research with our study system of over 170 adult males that associate in over 20 2nd order alliances.