NEW YORK — Chimpanzees in a midlife crisis? It sounds like a setup for a joke.
But there it is, in the title of a report published Monday in a scientific journal: "Evidence for a midlife crisis in great apes."
So what do these apes do? Buy red Ferraris? Leave their mates for some cute young bonobos?
"I believe no ape has ever purchased a sports car," said Andrew Oswald, an author of the study. But researchers report that captive chimps and orangutans do show the same low ebb in emotional well-being at midlife that some studies find in people.
That suggests the human tendency toward midlife discontent may have been passed on through evolution, rather than resulting just from the hassles of modern life, said Oswald, a professor of economics at the University of Warwick in England who presented his work Monday in the Proceedings of the National Academy of Sciences.
Several studies have concluded that happiness in human adults tends to follow a certain course between ages 20 and 70: It starts high and declines over the years to reach a low point in the late 40s, then turns around and rises to another peak at 70. On a graph, that's a U-shaped pattern. Some researchers question whether that trend is real, but to Oswald the mystery is what causes it.
"This is one of the great patterns of human life. We're all going to slide along this U for good or ill," he said. "So what explains it?"
He and co-authors assembled data on 508 great apes from zoos and research centers in the U.S., Australia, Canada, Singapore and Japan.
Caretakers and other observers had filled out a four-item questionnaire to assess well-being in the apes. The questions asked such things as the degree to which each animal was in a positive or negative mood, how much pleasure it got from social situations, and how successful it was in achieving goals.
The raters were even asked how happy they would be if they were the animal for a week.
Sounds wacky? Oswald and his co-authors say research suggests it's a valid approach. And they found that the survey results produced that familiar U-shaped curve, adjusted to an ape's shorter lifespan.
"We find it for these creatures that don't have a mortgage and don't have to go to work and don't have marriage and all the other stuff," Oswald said. "It's as though the U shape is deep in the biology of humans" rather than a result of uniquely human experiences.
Yes, apes do have social lives, so "it could still be something human-like that we share with our social cousins," he said. "But our result does seem to push away the likelihood that it's dominantly something to do with human life."
Frans de Waal, an authority in primate behavior at Emory University, cautioned that when people judge the happiness of apes, there may be a "human bias." But in an email he called the results "intuitively correct" and said the notion of biological influence over the human pattern is "an intriguing possibility."