Image credit: Lincoln Park Zoo (CC BY 4.0)
Like humans, animals have distinct personalities. Our close evolutionary cousins chimpanzees even display the same five major personality traits that we do – extraversion, neuroticism, conscientiousness, openness, and agreeableness – as well as a distinct trait, for dominance.
How did these distinct personality traits evolve and persist across different species? Ultimately, each trait must provide some fitness benefits that help the animal to reproduce and pass on the trait to its offspring. Longevity is an important factor in promoting fitness; an animal that lives for longer will have more opportunities to reproduce. Previous work in humans and other animals suggested that some personality traits are associated with a longer life. However, few studies have been large enough to test all major personality traits in both sexes of an animal species.
Altschul et al. used data from a long-term study of 538 captive chimpanzees to investigate possible associations between longevity and personality traits. The personalities of the chimpanzees started being rated between seven and 24 years ago. Since then, 187 of the chimpanzees have died.
Altschul et al. found that different personality traits were associated with longer life in males and females. Male chimpanzees with higher levels of agreeableness – the personality trait characterized by low aggression and positive social interactions such as cooperation – generally lived for longer. Female chimpanzees who were more open to new experiences also appeared to live for longer, but this apparent association may be influenced by age. Like humans, chimpanzees become less open to experiences as they become older.
No other personality traits appear to be linked to lifespan in chimpanzees. However, evidence suggests that conscientiousness and neuroticism can influence lifespan in humans. These two traits may therefore drive uniquely human behaviours that affect health.
The results presented by Altschul et al. suggest that human and ape agreeableness evolved through individuals who were able to achieve higher fitness by living longer. They also provide insights into how important personality and life history are to the health and survival of captive animals. For a fuller understanding of how ape personality evolved, future work should explore longevity and fitness in wild chimpanzees, as well as in our other closest relatives, bonobos.
