NEW YORK (AP) — Chimpanzees going through 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 simply 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.
A second study in the journal looks at a younger age group and finds that happiness in youth can lead to higher income a few years down the road.
More on that later. Let's get back to those apes.
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?"
When he learned that others had been measuring well-being in apes, "it just seemed worth pursuing the hunch that the U might be more general than in humans," he said.
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."
Oswald said it's not clear what the evolutionary payoff might be from such discontent. Maybe it prods parents to be restless, "to help find new worlds for the next generation to breed," he said.
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."
Even happiness researcher Sonja Lyubomirsky of the University of California, Riverside, who thinks the U-shaped pattern in people is a statistical mirage, says she can't write off the ape result the same way. "I'm not really sure what it means," she said. "I am finding this very intriguing." Maybe it will spur more thinking about what's going on in both apes and humans, she said.
Oswald is also an author of a second report in the journal that finds new evidence that being happy can help young people earn more money later on. Prior research had also reached that conclusion, but Lyubomirsky and University of Virginia psychology professor Shige Oishi called the new work the best evidence yet.
"Wow," Oishi said in an email. "This is a very strong paper" in its approach.
Researchers drew on data from a huge sample of young Americans who were surveyed repeatedly. They were asked to rate their positive feelings such as happiness and hopefulness at age 16 and again at 18, and their satisfaction with life at 22. Researchers then compared their ratings with their income around age 29. The data came from nearly 15,000 participants at age 16, and at least 11,000 at the latter two ages.
Higher income at age 29 was consistently linked to greater happiness at the earlier ages. The least happy 16-year-olds, for example, went on to average about $10,000 a year less than the happiest. That disparity shrank by about half when the researchers statistically removed the effect of other influences such as ethnicity, health and education.
A happiness effect even appeared between siblings within their own families.
What's going on? Most likely, happiness raises productivity and helps a person work effectively with others, factors that promote success in the workplace, Oswald said. The study found that happier people were more likely to get a college degree and get hired and promoted.
Ed Diener, an authority on happiness research at the University of Illinois at Urbana-Champaign, said optimism probably plays a role because it helps people persist in their efforts and take on difficult goals. Since several studies, including his own, have now linked happiness to later income, that idea seems reliable, he said.
Parents should recognize that "the psychological well-being of their children is important in how well the kids will do in simple dollar terms later on," Oswald said. And unhappy people should realize that they might have to strive harder than others to focus on work and promotion rather than their unhappiness, he said.
Malcolm Ritter can be followed at http://www.twitter.com/malcolmritter