

Wild male orangutan in Sumatra. Photo by: Rhett A. Butler.

Homo sapiens are not alone in experiencing a dip in happiness during middle age (often referred to as a mid-life crisis) since great apes suffer the same according to new research in the Proceedings of the National Academy of Sciences (PNAS). A new study of over 500 great apes (336 chimpanzees and 172 orangutans) found that well-being patterns in primates are similar to those experience by humans. This doesn’t mean that middle age apes seek out the sportiest trees or hit-on younger apes inappropriately, but rather that their well-being starts high in youth, dips in middle age, and rises again in old age.

“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,” explains co-author Andrew J. Oswald in a press statement.

Scientists interviewed zookeepers, volunteers, and researchers working closely with chimps and orangutans in order to assess the apes’ well-being. Using a questionnaire that measures human well-being, but was modified for great apes, the scientists found that apes experience a fall in their well-being in their late twenties or early thirties, comparable to human middle age, which is around 45-50. The simple questionnaire included questions on mood, how much enjoyment the subject gets out of socializing, and how successful they are on completing their goals.

“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 scientists write. “These findings have implications across scientific and social-scientific disciplines, and may help to identify ways of enhancing human and ape well-being.”

The scientists write that they do not know yet why these changes occur, but current theories include changes in the brain during middle age or an evolutionary cause that selects for well-being in youth and old age.

“[Old and young] individuals, being satisfied at stages of their life where they have fewer resources to improve their lot, would be less likely to encounter situations that could be harmful to them or their kin,” the researchers theorize, but call for more studies to unpack why humans—and great apes—experience mid-life depressions.

CITATION:Alexander Weiss, James E. King, Miho Inoue-Murayama, Tetsuro Matsuzawa, Andrew J. Oswald. Evidence for a midlife crisis in great apes consistent with the U-shape in human well-being. PNAS. 2012.

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