The puzzle over why most people experience a mid-life crisis could be nearer to a solution following a study showing that chimpanzees and orang-utans share the same emotional slump in middle age.
Scientists have discovered that captive apes in zoos around the world suffer a similar mid-life dip in happiness and wellbeing that is widely experienced in men and women from different socio-economic groups.
The findings suggest that the mid-life crisis in humans, which has until now defied a rational and plausible explanation, could be due to an underlying biological phenomenon that we share with our closest living relatives – the apes.
The study, carried out on 508 chimps and orang-utans in zoos around the world, revealed that ape “happiness”, as measured by a rigorous set of criteria monitored by their keepers, follows the same distinctive U-shape curve seen in humans.
Young apes start out happy but as they grow older they suffer a gradual emotional descent into a depression-like slump before going through an increase in happiness again during the final few years of life, the study found.
Professor Andrew Oswald of Warwick University, who has been studying human happiness for 20 years, said the findings indicate a fundamental biological basis for the mid-life crisis in people, which he said has little to do with the economic trappings of middle age.
“We hoped to understand a famous scientific puzzle: why does human happiness follow an approximate U-shape through life?” Professor Oswald said.
“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 mid-life low, and they have none of those,” he said.
The apes in the study lived in zoos in the United States, Japan, Canada, Australia and Singapore. Their keepers were asked to fill in a standard questionnaire on ape behaviour that is widely accepted as a good measure of primate wellbeing, says the study published in the journal Proceedings of the National Academy of Sciences.
For both species and in all parts of the world where they lived, the results indicate a clear dip in wellbeing in mid-life, which turned out to be a near-perfect match for what also happens in humans.
“Our results imply that human wellbeing’s curved shape is not uniquely human and that, although it may be partly explained by aspects of human life and society, its origins may lie partly in the biology we share with great apes,” the study says.
Professor Oswald said that changes in human physiology with age, such as hormonal changes, may contribute to the mid-life crisis, although the menopause in women has been ruled out as a cause.
Previous theories to explain the ubiquity of human mid-life crises centred on the financial hardships of middle age, a rise in regret for lost opportunities, or a realisation that certain aspirations of life are in reality unattainable, the study says.
Professor Oswald said that the lack of data to support any of these theories led him to approach primatologist Alexander Weiss of the University of Edinburgh to see if there are any parallels in the animal kingdom
“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,” Dr Weiss said.
“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,” he said.
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