Chimpanzees and orangutans experience a mid-life crisis just like humans, according to a survey of 508 great apes in captivity shows.
The scientists published their findings in the journal Proceedings of the National Academy of Sciences. The sense of well-being in primates in their late 20s to mid-30s, which is the equivalent of middle age, is low before it rebounds in old age.
This could indicate that mid-life crises may not only affect humans, and that they could have a biological cause, rather than sociological.
Humans, regardless of their wealth or status, experience a dip in happiness at middle age, which occurs during the mid-30s to late 50s. Despite this almost universal phenomenon, scientists have struggled to identify the underlying cause of the dissatisfaction. Social and economic factors, like financial hardships and the failure to realize ambitions are probable causes.
Alexander Weiss, a psychologist at the University of Edinburgh, UK, and his colleagues, set out to see if there was a biological factor involved. They wanted to assess the well-being of captive chimpanzees and orangutans as judged by their keepers.
The apes in the study covered all age ranges, and their happiness was rated by a survey answered by the keepers, which covered four criteria: the animals’ overall mood, how much pleasure they got out of socializing, their success in achieving goals, and how happy the keeper would be if he or she were the animal for a week.
This survey is anthropomorphic, but Weiss states that it’s easy for someone who spends a lot of time with the apes to gauge their moods. Weiss’ previous work shows that well-being, when measured by different caretakers, is consistent, and partly based in inherited genetic factors.
Among the chimps and orangutans surveyed, the happiest tend to be the youngest and oldest, while the most dissatisfied seemed to be the ones in their mid-30s. The study didn’t follow any apes over time, meaning that there could be confounding factors like the early death of unhappy apes.
Other primatologists would have liked to see a more scientific approach when it comes to measuring ape happiness, such as stress hormone levels, but if they conclusions are real, they could have implications for humans as well.
Unhappiness can be a catalyst for change, spurring unhappy adults to act more adaptively by seeking out new mates. However, any explanation remains speculative.
Reference: “Evidence for a midlife crisis in great apes consistent with the U-shape in human well-being” by Alexander Weiss, James E. King, Miho Inoue-Murayama, Tetsuro Matsuzawa and Andrew J. Oswald, 19 November 2012, Proceedings of the National Academy of Sciences.