Rival teams of male dolphins form animal world’s largest social networks, long-running study finds | Science


Anthropologists have long celebrated and questioned the ability of humans to cooperate. Our particular talent lies in forming interlocking cooperative networks that involve unrelated individuals: family, community, city, state, nation, and allied nations. Even our closest relative, the chimpanzee, doesn’t. But over the past 4 decades, researchers have shown that another animal does: the Indo-Pacific marine bottlenose dolphin (Tursiops aduncus) from Shark Bay in Western Australia.

Unrelated male dolphins deploy their social intelligence to build complex alliances that increase their chances of reproductive success. A new study concludes that they are the largest cooperative societies as complex outside of humans. Moreover, they seem to have evolved in a different way from ours. “This is an exciting finding that helps bridge the huge perceived gap between humans and other animals,” says Mauricio Cantor, a behavioral ecologist at Oregon State University who was not involved in the study.

In a Dolphin Society exploration launched in 1982, behavioral ecologist Richard Connor, now affiliated with Florida International University, and his team tracked more than 200 male dolphins in the exceptionally clear waters of Shark Bay, recording which males pass the most time together. . Over the years, they’ve discovered that men form close relationships with one or two other men and that these partnerships are interwoven into a larger alliance, which in turn is interwoven into another alliance – kind of like being member of “a platoon, a company and a regiment,” notes Harvard University primatologist Richard Wrangham, who is not part of the team. Male dolphins cooperate to capture and defend fertile female dolphins from others groups of males A single male cannot surround a female, he needs partners.

In the new study, the team analyzed data collected between 2001 and 2006 on 121 individual men, revealing a super-connected social network with each man connected to each other, directly or indirectly. Males even cultivate relationships with males outside of their alliances on three levels, forming the largest known network of any non-human speciesand thereby increasing their reproductive success, researchers report today in the Proceedings of the National Academy of Sciences. Each male had an average of 22 allies; some had as many as 50.

Male dolphins form bonds by swimming and diving side by side, stroking, holding flippers, having sex, hissing to each other when separated, forming “teams” and helping out to each other if rivals try to drive a female away. Those with the strongest social bonds spend the most time with females, increasing their chances of mating. “They make strategic social decisions,” says Connor, who suspects that dolphins use their big brains in part to remember which individuals came to their aid and which fled during the fights.

Cooperation is not exactly uncommon in the animal kingdom – animals from social insects to lions, wolves and spotted hyenas, and many primates cooperate; some, like chimpanzees and bonobos, even do this with non-relatives. (And Unrelated female bonobos have recently formed coalitions with strangers against men). But none of these species form “multilevel alliances to achieve goals,” says Athena Aktipis, a cooperative theorist at Arizona State University. “It’s interesting and cool what dolphins do.”

Wrangham adds that Connor’s decades-long study provides one of the most compelling arguments for the “social brain hypothesis,” the idea that the need to track many social relationships has led to the evolution of big brains and intelligence. Dolphins provide “a dramatic demonstration of the positive correlation between brain size and social complexity,” he says.

Anthropologists have argued that human intergroup cooperation is unique and linked to the evolution of bonds between men and women and the role of men in caring for offspring. These long-lasting pair bonds lead to extensive social networks because both partners have parents interested in ensuring the survival of their genes. But in dolphins, as in chimpanzees, males and females do not form long-lasting pairs and males do not help with parenting. “Our results show that intergroup alliances can emerge without these behaviors and from a social and mating system that more closely resembles that of chimpanzees,” says Connor.

In other words, these very complex alliances can evolve in several ways, says Frans de Waal, primatologist emeritus at Emory University. “It’s good to think about the fact that there can be several evolutionary paths towards this result.”


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