Human behaviour studies have revealed the well-established trend that our level of happiness declines after childhood until middle age, when we gradually begin to feel more content again.
Now, researchers have discovered that, as in humans, chimpanzee and orangutan well-being or happiness follows a U shape and is high in youth, falls in middle age, and rises again in old age.
The study set out to test the theory that the pattern of human well-being over a lifespan might have evolved in the common ancestors of humans and great apes.
An international team of researchers studied 508 great apes housed in zoos and sanctuaries in the US, Japan, Canada, Australia and Singapore.
The apes' well-being was assessed by keepers, volunteers, researchers and caretakers who knew the apes well. Their happiness was scored with a series of measures adapted from human subjective well-being measures.
"We hoped to understand a famous scientific puzzle: why does human happiness follow an approximate U-shape through life? We ended up showing that it cannot be because of mortgages, marital breakup, mobile phones, or any of the other paraphernalia of modern life. Apes also have a pronounced midlife low, and they have none of those," said, Professor Andrew Oswald from the University of Warwick.
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"Based on all of the other behavioural and developmental similarities between humans, chimpanzees, and orangutans, 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," said Dr Alex Weiss from the University of Edinburgh.
Researchers said their findings do not rule out the possibility that economic events or social and cultural forces contribute part of the reason for the well-being U shape in humans.
However, they highlight the need to consider evolutionary or biological explanations.
For instance, individuals being satisfied at stages of their life where they have fewer resources to improve their lot may be less likely to encounter situations that could be harmful to them or their families.
The study was published in the Proceedings of the National Academy of Sciences.