The secret to a long life is getting along with your peers and taking care of family, at least for captive male chimpanzees, a new study has found. For female chimps, the results were less clear-cut, but its possible an exploratory nature makes for a longer life, as well as a more interesting one. The relevance to humans remains to be seen, but these aren't bad rules to live by.
Scientists studying animal psychology rate them using the same personality traits used to describe humans, and have noted that chimpanzees show a spread more similar to us than other near relatives, such as bonobos. Assessments made by keepers at zoos and wildlife parks over the last 24 years have been collected by Dr Drew Altschul of the University of Edinburgh. In that time, 187 of the chimpanzees have died, providing a sufficient sample to test the traits that extend or shorten life under these conditions.
Most notably, agreeableness, which Altschul and co-authors describe in eLife as “[t]he personality trait characterized by low aggression and positive social interactions such as cooperation,” was associated with longer life for males, but made no difference for females.
Female chimpanzees that were more open to new life experiences also appeared to live longer, but the authors are hesitant on this conclusion. “Like humans, chimpanzees become less open to experiences as they become older,” they write. With a large sample assessing personality traits throughout the chimpanzees' lives, it would be possible to establish whether the effect is real, but the limited snapshots available to the team mean younger chimps' longer life expectancies could be inducing a false result.
No other aspects of the chimpanzees' personalities appeared to affect their longevity. In contrast, humans who score high for extraversion and conscientiousness and low for neuroticism usually live longer.
If a personality trait has a major effect on an animals' prospects for evolutionary success, it will spread quickly through the population. Consequently, when high diversity implies competing forces maintaining an equilibrium.
In this case, the authors think agreeable (male) apes may be less likely to succeed in their attempts to mate when young, but live long enough to get second chances or to care for those offspring they do have. If the openness benefit for females is real, it would be harder to explain.
Of course, since these assessments are made in an artificial environment, we can't be sure they reflect how things would pan out in the wild. Unfortunately, despite the astonishing work done studying chimpanzee personalities in their native habitat, we lack an equivalently large and detailed database to test if the same results apply there. Moreover, modern threats like trapping may skew results compared to historical patterns.