Rob is a risk taker—the kind of guy who climbs mountains just because they are there. And he’ll be the first to tell you that he does it for the rush. Kristin is more reserved, but don’t ask her about that, because she’s not a talker. Adrian is always happy; Steve takes offense when none is intended. They all have different personalities.
Psychologists usually define personality in terms of the expression of stable, enduring behavioral patterns. One of the most studied personality traits is shyness. People who are shy when they are young are very likely to be shy for their entire lives.
Every human society is a composite of different personality types. A mix of personalities makes for a more pleasant society, perhaps even a more functional one. A society of pure risk takers probably would not last long, nor would a society composed completely of shy folks.
But human societies are not unique in containing a mixture of different personality types. Of late, evolutionary behaviorists have turned to studying animalities. More and more evidence, from a wide variety of species—cats, dogs, hyenas, and many other critters—suggests that animals within a given population show consistent differences in how they behave, and that these differences often map nicely onto the sorts of patterns we see in humans. But animal behaviorists like me are interested in much more than whether animals and humans show similar animality/personality types. We want to understand the costs and benefits associated with different animal temperaments.
You may have wondered what it means for an orangutan to be a happy-go-lucky sort. Alexander Weiss and his colleagues have. And their sortie into simian bliss has shed new light on animalities. Psychologists have long used a certain questionnaire to measure what they call “subjective well-being” in humans. Trained observers watch someone, looking for signals of positive or negative mood, and they try to gauge how much pleasure the subjects they are watching derive from interacting with others. They note whether the people they are observing are good at achieving their goals. Then they fill out the questionnaire. Weiss and his colleagues took this scale and “orangutanized” it for apes living in zoos. They measured such things as how well the orangutans interacted with one another and with their zookeepers, the frequency of negative versus positive moods displayed, and the animals’ ability to achieve a goal. Over the course of seven years, they measured subjective well-being in 172 orangutans.
They found that if you’re an orangutan, at least an orangutan living in a zoo, you have basically one of two animality types. If you are lucky, you’re an orangutan who scored high on the subjective well-being test. Such individuals were extroverts, interacting often and in positive ways with the other apes, whether their fellow orangutans or their human keepers. Other orangutans scored poorly on the subjective well-being test—they didn’t play well with others. Additional studies showed that these animals displayed unusual “neurotic” behaviors—they seemed uncertain of themselves and distressed by events that do not trouble other orangutans.
Subjective well-being mattered for the orangutans, and it mattered a lot. When Weiss and his team looked at mortality data, they found orangutans that were rated high on subjective well-being measures lived an average of 11 years longer than those who rated low.