Mammals that live in groups tend to live longer than solitary species, new research on nearly 1,000 different animals shows.
Scientists from China and Australia compared 974 mammal species by analyzing longevity and how they tend to be socially organized.
Classifying mammals into three categories – solitary, pair-dwelling and group-dwelling – the researchers found that group-dwelling animals such as elephants and zebras tended to live longer on average than solitary species such as the anteater and eastern chipmunk.
The correlation held even when the researchers took into account the relationship between larger species size and longer lifespans.
The maximum lifespan of mammals varies from about two years in humpback whales to more than 200 years in bowhead whales.
Northern short-tailed deer – which are solitary animals – and gregarious great horseshoe crabs are similar in weight, for example, but live a maximum of about two and 30 years, respectively.
The researchers also performed a genetic analysis for 94 species and identified 31 genes that are associated with both social organization and longevity.
The genes are mostly related to immunity and hormones, the latter of which the study authors say may play a role in social behavior.
The authors of the study suggest that “living in a group reduces external mortality by limiting the risks of predation and starvation, and the strong and stable social bonds formed between group members have the power to increase longevity.”
“These benefits are expected to overcome the costs inherent to group living, such as competition for mating partners and food, stress from superior individuals, and the spread of infectious diseases through social contact,” they wrote.
Previous studies of specific group-living species, such as chakma baboons, have found that individuals with strong social bonds live longer than those with weaker and less stable bonds. Scientists have documented similar findings in rhesus macaques.
But sociality seems to play a different role in animals that don’t necessarily live in groups. A 2018 report on yellow-bellied marmots – a “socially flexible” species – links strong social bonds to reduced longevity.
Whether longevity confers any evolutionary advantage is debatable. Associate Professor Celine Frere, an evolutionary biologist at the University of Queensland, who was not involved in the research, said some short-lived animals reproduce much faster than longer-lived species.
“Group living reduces external mortality by limiting the risks of predation and starvation,” the study authors wrote. Photo: Anadolu Agency/Getty Images
“From an evolutionary context, what an individual seeks to do is pass on their genes to future generations,” she said. “An animal that lives for two years, compared to a whale that lives for 200 years, is most likely to have produced the same amount of offspring in its lifetime.”
Frere said the study’s findings are interesting, but categorizing species as solitary, pair-living or group-living is “a simplistic approach to looking at social organization.”
“They want to imply that gregarious species live longer. But it’s much more complicated than that. [Lifespan] is related to their ecology. It has to do with their reproductive biology, it has to do with their mating system.
“Whether you are a solitary animal or a group animal, you have to learn to live with others … and you will compete with others for access to resources.”
Frere added that social organization varies greatly among group-living mammals, ranging from highly structured dominance hierarchies to fission and fusion societies in which the size and composition of social groups change over time.
The research was published in the journal Nature Communications.
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