Forty- and 50-somethings in the throes of a mid-life crisis should probably stop blaming a troubled marriage, their kid's college costs, or technology that makes them feel about as modern as papyrus compared to their younger colleagues.

A new study finds that chimpanzees and orangutans, too, often experience a mid-life crisis, suggesting the causes are inherent in primate biology and not specific to human society.

"We were just stunned" when data on the apes showed a U-shaped curve of happiness, said economist Andrew Oswald of the University of Warwick in England and a co-author of the paper, which was published on Monday in the Proceedings of the National Academy of Sciences of the US.

In what Oswald, 58, calls "a burst of madness," since no such study had ever been attempted, he and his colleagues decided to see whether creatures that don't have career regrets or underwater mortgages might nevertheless suffer a well-being plunge in middle age.

They enlisted colleagues to assess the well-being of 155 chimps in Japanese zoos, 181 in US and Australian zoos and 172 orangutans in zoos in the US, Canada, Australia and Singapore. All three groups of apes experienced mid-life malaise: a U-shaped contentment curve with the nadir at ages 28, 27 and 35, respectively, comparable to human ages of 45 to 50.

Why would chimps and orangutans have a mid-life crisis? It could be that their societies are similar enough to the human variety that social, and not only biological, factors are at work, Oswald said. Perhaps apes feel existential despair, too, when they realize they'll never be the alpha male or female.

"Maybe nature doesn't want us to be contented in middle age, doesn't want us sitting around contentedly with our feet up in a tree," he said. 

Reuters