Rival teams of male dolphins form the largest social networks in the animal world, long-term study finds | Science

Anthropologists have long celebrated and puzzled over humans’ ability to cooperate. Our special talent lies in the formation of nested cooperative networks that involve unrelated individuals: family, community, city, state, nation and allied nations. Even our closest relative, the chimpanzee, does not do this. But over the past 4 decades, researchers have shown that another animal does: the Indo-Pacific marine abalone (Tursiops aduncus) from Shark Bay in Western Australia.

Male dolphins, who are not related to each other, use their social intelligence to form complex alliances that increase their chances of reproductive success. A new study concludes that these are the largest such complex cooperative societies outside of humans. What’s more, they seem to have evolved differently than ours. “This is an exciting discovery that helps bridge the huge, perceived gap between humans and other animals,” said Mauricio Cantor, a behavioral ecologist at Oregon State University who was not involved in the study.

In a study of dolphin society that began in 1982, behavioral ecologist Richard Connor, now affiliated with Florida International University, and his team tracked more than 200 male dolphins in the ultra-clear waters of Shark Bay, recording which males spent the most time together. Over the years, they have found that men form close relationships with one or two other men, and that these partnerships are embedded in a larger alliance, which in turn is embedded in yet another alliance—rather like a member of a “platoon, company and regiment,” notes Harvard University primatologist Richard Wrangham, who was not part of the team. Male dolphins cooperate to capture and protect fertile female dolphins from other groups of males. A single male cannot collect a female; needs partners.

In the new study, the team analyzed data collected between 2001 and 2006 on 121 individual men, revealing a hyperconnected social network with each man connected directly or indirectly to one another. Males even cultivate bonds with males outside their unions at three levels, forming the largest network known in any nonhuman species, and thus increase their reproductive success, researchers report today in Proceedings of the National Academy of Sciences. Each male had an average of 22 allies; some had as many as 50.

Male dolphins bond by swimming and diving side by side, caressing, holding flippers, having sex, whistling to each other when separated, forming “teams” and coming to the rescue if rivals try to kidnap the female. Those with the strongest social bonds spend the most time with females, thus increasing their chances of reproduction. “They make strategic social decisions,” says Connor, who suspects that dolphins use their large brains in part to remember which individuals came to their aid and which fled during fights.

Cooperation is not uncommon in the animal kingdom – animals from social insects to lions, wolves and spotted hyenas, as well as many primates cooperate; some, like chimpanzees and bonobos, even do it with non-relatives. (And recently, unrelated female bonobos have been reported to form coalitions with outsiders against males). But none of these types form “multilevel alliances to achieve goals,” says Athena Aktipis, a cooperation theorist at Arizona State University. “It’s interesting and cool what dolphins do.”

Wrangham adds that Connor’s decades-long study represents some of the most compelling support for the “social brain hypothesis,” the idea that the need to keep track of multiple social relationships led to the evolution of large brains and intelligence. Dolphins provide “a dramatic demonstration of the positive relationship between brain size and social complexity,” he says.

Anthropologists argue that human intergroup cooperation is unique and related to the evolution of male-female relationships and the role of men in caring for offspring. These long-lasting pair bonds lead to extended social networks because both partners have relatives interested in ensuring the survival of their genes. But in dolphins, as in chimpanzees, males and females do not form permanent pairs and males do not assist in parenting. “Our results show that intergroup alliances can emerge without these behaviors and from a more chimpanzee-like social and mating system,” Connor says.

In other words, there’s more than one way for these highly complex alliances to develop, says Frans de Waal, a primatologist emeritus at Emory University. “It’s nice to think that there could be multiple evolutionary paths to this outcome.”

Leave a Comment