We already know that human beings and apes have much in common – not least our interest in tablet computers—but a new study by a team of international researchers shows that we are far more alike than we ever thought.

DIETER NAGL/AFP/Getty Images 33 year-old female Orangutan 'Nonja' is watched by visitors on June 8, 2009 in Vienna's Schoenbrunn Zoo.

We already know that human beings and apes have much in common – not least our interest in tablet computers—but a new study by a team of international researchers published this week shows that we are far more alike than we ever thought. Apes, you see, also suffer from midlife crises.

The scientists observed 508 great apes in captivity. They found that similar to humans, the apes experienced a high level of well-being in youth which fell to a nadir in midlife, before rising again in old age.

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The midlife crisis usually occurs somewhere between the mid-thirties and late fifties in human beings, marked by a sense of ennui and ambivalence about what lies ahead in life. Symptoms include buying flashy cars, leaving their partners for a much younger model, or a change in career. Some regard it as a cliché of modern life, yet social scientists have not been able to explain why we experience it, and why it is such a universal phenomenon.

Until now, studies into well-being have focused solely on human beings, resulting in what the researchers call a “strictly human-centered and socioeconomic explanation” for the mid-life dip. Given that the apes feel it too, the answers may have a biological explanation rather than socioeconomic.

Published in the Proceedings of the National Academy of Sciences, the researched looked at chimpanzees and orangutans of various ages and gender in zoos and sanctuaries around the world.

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Using a questionnaire adapted for non-human primates, the researchers asked zoo keepers and others who worked closely with the primates questions such as “how successful do you think the subject (the ape) is in achieving its goals?” and “how happy would (you) be if (you) were the subject for a week?”

Explaining the findings to BBC Nature, lead author Alexander Weiss of the University of Edinburgh said:

“You don’t have the chimpanzee hitting mid-life and suddenly they want a bright red sports car. But there may be other things that they want like mating with more females or gaining access to more resources.”

Frans de Waal, a primatologist at Emory University in Atlanta, Georgia, explained to Nature that while it may have been better for the researchers to include more concrete indicators such as stress hormone levels, the conclusions of the study could help all primates. “It may well be that certain physical characteristics, hormone levels or emotion-regulation skills play a role,” he said.

While we may be closer, then, to figuring out the causes of the mid-life crisis, speculation remains open as to why anyone has it at all. The researchers suggest its causes could be anything from an evolutionary need to get better at setting more achievable goals as we age, to the unhappy possibility that unhappy primates are more likely to die sooner.

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