Evidence for a midlife crisis in great apes consistent with the U-shape in human well-being.

Alexander Weiss, James E. King, Miho Inoue-Murayama, Tetsuro Matsuzawa, Andrew J. Oswald
DOI: 10.1073/pnas.1212592109


Recently, economists and behavioral scientists have studied the pattern of human well-being over the lifespan. In dozens of countries, and for a large range of well-being measures, including happiness and mental health, well-being is high in youth, falls to a nadir in midlife, and rises again in old age. The reasons for this U-shape are still unclear. Present theories emphasize sociological and economic forces. In this study we show that a similar U-shape exists in 508 great apes (two samples of chimpanzees and one sample of orangutans) whose well-being was assessed by raters familiar with the individual apes. This U-shaped pattern or “midlife crisis” emerges with or without use of parametric methods. Our results imply that human well-being’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. These findings have implications across scientific and social-scientific disciplines, and may help to identify ways of enhancing human and ape well-being.


This research finds evidence of a ‘mid-life crisis’ in Great Apes. Chimpanzees and orangutans follow the same U-shaped pattern of well-being through life as humans, so both apes and human beings share a ‘mid-life crisis’. This is the finding from a new study, published in the Proceedings of the National Academy of Sciences of the USA that 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. The authors show that, as in humans, chimpanzee and orang-utan well-being (or happiness) is high in youth, falls in middle age, and rises again into old age. A multi-disciplinary, international team of researchers, led by psychologist Dr Alex Weiss from the University of Edinburgh, studied 508 great apes housed in zoos and sanctuaries in the United States, 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. The study is the first of its kind and the authors knew their work was likely to be unconventional. Dr Weiss said: “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. 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.”
The team included primatologists and psychologists from Japan and the United States. In the paper the team point out that 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 example, 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.

Article Information
Weiss A, King JE. , Inoue-Murayama M, Matsuzawa T, Oswald AJ. (2012)Evidence for a midlife crisis in great apes consistent with the U-shape in human well-being. Proceedings of the National Academy of Sciences, 109(49): 19949-19952. https://dx.doi.org/10.1073/pnas.1212592109