Friendship among mountain gorillas can pay off in some ways while creating new risks in others, according to a new long-running field study tracking health and reproduction. Researchers say the mixed outcomes may help explain why some individuals are more sociable than others.
The analysis drew on more than 20 years of observations of 164 wild mountain gorillas in Volcanoes National Park, Rwanda. Scientists compared patterns of close social bonds with measures including illness, injuries from conflict and reproductive success.
Benefits shift with group size
The study found that the advantages of social ties depended heavily on a gorilla’s group environment, including group size and stability. What looked beneficial in one setting could become costly in another as competition and exposure to disease changed.
For females, strong and stable relationships were generally linked to less illness, but the pattern was not uniform across groups. In smaller groups, more socially connected females tended to fall ill less often but also had fewer offspring.
In larger groups, the relationship appeared to flip in important ways, with friendly females showing higher birth rates while also experiencing illness more frequently. Researchers suggested that crowded social settings may increase exposure to pathogens even as they improve access to support and mating opportunities.
Male bonds trade illness for safety
For males, tight social bonds were associated with getting ill more often, but those connections also came with a protective effect. Well-bonded males were less likely to be injured in fights, a major threat in a species where conflict can be severe.
Lead author Robin Morrison of the University of Zurich said the findings suggest it is not simply a case of more social contact causing more disease. One possibility raised by the team is that maintaining close ties may carry energetic and stress-related costs for males, potentially affecting immune function.
The work, conducted with the Dian Fossey Gorilla Fund and researchers at the Universities of Exeter and Zurich, underscores how social behaviour can be shaped by competing pressures. The authors argue that there may be no single best social strategy, because the optimal level of sociability shifts with sex, group context and life stage.
The paper was published in the Proceedings of the National Academy of Sciences and adds to broader evidence that social environments can strongly influence health and lifespan across social mammals, including humans. At the same time, it cautions against assuming that more friends is always better, even in highly social species.
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