Proceedings of the National Academy of Sciences, 109(49): 19949-19952


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

アレキサンダー・ワイス教授(英国エジンバラ大学)、松沢哲郎教授(京都大学霊長類研究所)、村山美穂教授(京都大学野生動物研究センター)らの研究グループによる 研究成果が、2012年11月19日発行の米科学アカデミー紀要に掲載されました。

類人猿(チンパンジーとオランウータン)でも、 人間と同様に中年の時期に幸福度が下がる、という調査結果の報告です。 対象は、チンパンジー336個体、オランウータン172個体、合計508個体です。 日米など5か国の動物園等の施設で飼育されています。 その飼育にかかわる人々に、 それぞれの個体の個性の評定をしてもらいました。 前向きか、社交的か、目的を遂行するか、 そして「もし彼らだったとしたら自分は幸せと思うか」という 問いについて答えてもらいました。それぞれの個体について2人が評定します。 その結果をもとに幸福度を定義してみると、 30歳頃(ヒトでいえば45歳ころ)を最低としたU字型になりました。 すなわちチンパンジーやオランウータンでも中年になると、 傍目にみて幸福とはみえませんでした。 人間は、中年の時期に幸福度がさがることが知られています。 中年の危機、と呼ばれています。 これまでは、社会的・経済的要因でそうなると考えられてきました。 今回の結果からみて、そもそもそうした中年の危機は、 生物学的な要因があり、ヒト科に共通の現象と考えられます。 ちなみに、日本のチンパンジー12施設の155人のチンパンジー が研究対象に含まれています。

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.
Alexander Weiss

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. doi: 10.1073/pnas.1212592109