Here's another sign that great apes are more like us than we might think. A new study suggests apes can have a mid-life crisis.
Researchers looked at the well-being and happiness of more than 500 chimpanzees and orangutans of varying ages, from zoos, sanctuaries and research centres.
The apes were assessed by zoo keepers, researchers and caretakers who had worked with them for at least two years and knew how they acted.
The researchers say the apes showed a similar pattern to the "U-shape curve" of happiness, that studies have found in people.
In other words, they were happy in their youth... reached a low point in middle age... and became happier in their old age.
For a long time, the idea of a mid-life crisis was thought to be unique to people - in part because of the hassles and routine of day to day life.
Not anymore says Dr. Alexander Weiss of the University of Edinburgh and the lead author of the study.
"What [this study] says is that it may be a part of the picture, but it's clearly not all of the picture," he told BBC Nature.
"We have to look deeper into our evolutionary past and that of the common ancestors that we share with chimpanzees, orangutans and other apes."
Dr. Andrew Oswald - another of the researchers - has studied human happiness for 20 years.
He says it was "mind-blowing" to find mid-life crises in apes, which suggests they're biological and physiological.
Maybe, even something that was passed on through evolution.
"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.
During the study, the apes were given a score for well-being and happiness on a short questionnaire - which was based on a model for people but designed for primates.
The questionnaire looked at several factors including how happy or sad the ape appeared, how much it pleasure it got from social situations, and how successful it was in achieving goals.
The researchers say they found chimpanzees face similar social pressures and stress factors as people do.
Dr. Weiss did point out one difference. "You don't have the chimpanzee hitting mid-life and suddenly they want a sports car."
Maybe not. But how do scientists explain this.