Long-distance swimming may have opened up a world of complexity for dolphins.
Male bottlenose dolphins in Shark Bay, Western Australia, cooperate in groups of two or three. These groups also link with others to form gangs of up to 14 males, and sometimes two or more large gangs coalesce.
Such complex alliances usually form to control either territory or sexual partners. Richard Connor of the University of Massachusetts Dartmouth tracked 120 males in the bay and found no evidence that dolphins form the groups for either reason, suggesting their society is unusually open.
Humans and elephants also form complex groups. As with dolphins, they use little energy to travel vast distances, hinting that this contributed to the evolution of complex social networks.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2012.0264