Coles, Jeremy. “Great Apes May Have ‘Mid-Life Crisis,’ A Study Suggests.” BBC Nature, Nov. 19, 2012.

Chimpanzees and orangutans may experience a "mid-life crisis" like humans, a study suggests.

An international team of researchers assessed the well-being and happiness of the great apes. They found well-being was high in youth, fell to a low in midlife and rose again in old age, similar to the "U-shape curve" of happiness in humans. The study brought together experts such as psychologists, primatologists and economists. Results are published in the Proceedings of the National Academy of Sciences.

"What we are testing is whether the U-shaped curve can describe the association between age and well-being in non-human primates as it does in humans," psychologist and lead author Dr Alexander Weiss of the University of Edinburgh told BBC Nature. Dr Weiss hoped the results would show a similar curve because of the close relationship between humans, chimpanzees and orangutans. The study showed that male and female humans, chimpanzees and orangutans have the same U-shaped curve despite differences in social roles, and the phenomenon is therefore not uniquely human.

The sample subjects included 508 chimpanzees (Pan troglodytes) and orangutans (Pongo sp.) of varying ages, from zoos, sanctuaries and research centers. They were assessed by zoo keepers, volunteers, researchers and caretakers who had worked with the primate subject for at least two years and knew its behavior. The animals were numerically scored for well-being and happiness on a short questionnaire, which was based on a human well-being model but modified for use in non-human primates.

Dr Weiss said that the similarities between humans, chimps and orangutans go beyond genetics and physiology. For example, chimpanzees face similar social pressures and stress factors to humans. "You don't have the chimpanzee hitting mid-life and suddenly they want a bright red sports car," explained Dr Weiss. "But there may be other things that they want like mating with more females or gaining access to more resources."

Co-author Andrew Oswald, professor of economics at the University of Warwick, has researched human happiness for 20 years. "One of the reasons we decided to look at ape data was that when you study humans, that U-shape is exactly the same when you adjust statistically for things like education, income and marriage. For Prof Oswald it was "quite mind-blowing... to find it in apes."

The study showed that orangutans may experience a midlife dip in well-being and happiness
He concluded that "the mid-life crisis is real and it exists in... our closest biological relatives, suggesting that it is probably explained by biology and physiology."

Psychologist Dr Weiss said that this research opens a lot of doors. He explained that for a long time this kind of mid-life crisis was considered something specific to human society and human lives. "And what [this study] says is that it may be a part of the picture, but it's clearly not all of the picture. We have to look deeper into our evolutionary past and that of the common ancestors that we share with chimpanzees, orangutans and other apes."