So what do these apes do? Buy red Ferraris? Leave their mates for some cute young bonobos? Uh, no.
"I believe no ape has ever purchased a sports car," said study author Andrew Oswald.
But researchers report that captive chimps and orangutans show the same low ebb in emotional well-being at mid-life that some studies find in people.
That suggests the human tendency toward mid-life discontent may have been passed on through evolution, rather than from the hassles of modern life, said Oswald, a professor of economics at the University of Warwick in England who presented his work 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.
He and co-authors assembled data on 508 great apes from zoos and research centers in the US, Australia, Canada, Singapore and Japan.
"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."
Oswald is also an author of a second report that finds new evidence that being happy can help young people earn more money later on. Researchers studied a group of Americans when they were 16, 18 and 22. Higher income at age 29 was consistently linked to greater happiness at the earlier ages. The least happy appeared to be 16-year-olds who went on to average about $10,000 a year less than the happiest.