Scientists have discovered that chimpanzees and orang-utans can experience a mid-life crisis just as humans do.
A study of 508 captive chimpanzees and orang-utans from around the world found the animals' sense of well-being was highest in youth and old age, but dipped in middle age.
The same U-shaped curve of happiness is seen in humans, who appear most content early and late in their lives.
Lead researcher Professor Andrew Oswald, from the University of Warwick, said: "We hoped to understand a famous scientific puzzle: why does human happiness follow an approximate U-shape throughout life?
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"We ended up showing that it cannot be because of mortgages, marital break-up, mobile phones, or any of the other paraphernalia of modern life. Apes also have a pronounced mid-life low and they have none of those."
The scientists, whose findings are published in the journal Proceedings of the National Academy of Sciences, adapted a questionnaire widely used to measure human well-being.
Zookeepers, researchers and caretakers who knew the apes well were asked to provide mood rating scores for the animals they looked after.
Both male and female apes were assessed and both appeared to suffer a drop in happiness at around the age of 40 to 50, in human years.
The results indicate that evolutionary and biological factors may play a part in a human mid-life crisis, as well as economic events or social and cultural forces.
Co-author Dr Alex Weiss, from the University of Edinburgh, said: "Based on all of the other behavioural and developmental similarities between humans, chimpanzees and orang-utans, we predicted that there would be similarities when looking at happiness over the lifespan, too."
"However, one never knows how these things will turn out, so it's wonderful when they are consistent with findings from so many other areas."