#140 Do Apes Have a Mid-Life Crisis?
Ageing Wellbeing
The idea that there is a slump in our wellbeing in mid-life is well accepted. Do apes have the same problem? Does wellbeing then increase forever?
A Five-Minute Read
It was ten years ago that a team of scientists published a study in a prestigious international journal. The team asked zookeepers all over the world to answer a questionnaire for each ape under their care. They evaluated the ape along different dimensions of well-being. They asked about the apes mood. How much they enjoyed socializing,. They were asked to evaluate the ape's reaction to success or failure in the tasks they undertook. Finally they asked each keeper how they would feel about being that particular ape for a week. They scored that feeling on a seven point positive to negative scale.
In total some 500 apes were assessed in this way. They came from multiple zoos all over the world. When they related the resultant wellbeing scores to age the results were surprising. Wellbeing fell in the middle age and climbed again in old age. Many of these animals can live to 50 years in captivity. The pattern was the same as found in humans across many different cultures and societies.
It had always been surmised that human mid-life crises came from social factors. From the financial and social pressures of raising children. From the need to take care of parents. From the emerging sense that careers had stagnated. Obviously none could apply to the great apes. Instead the researchers began to speculated about physical changes. Did changes in the body account for the mental state. Needless to say the results produced a heated debate in the academic community.
The Paradox of Wellbeing
Average life satisfaction is high at younger ages. It falls and reaches a minimum at about age 40, which is sometimes called the “midlife crisis”. It then increases year on year. This U-shaped pattern has been confirmed in many datasets and across many countries. In a previous Newsletter I reported the results of one of these studies. It is a reassuring idea for those who have passed the low point. It does, however, raise problems when tested against reality. Older people face many challenging life events. They do develop chronic diseases. They will lose friends and even spouses. They may have financial worries. How then does wellbeing continue to increase. This has been dubbed the “paradox of wellbeing”.
The answer lies in a topic that is a theme of many of these Newsletter. These findings come from cross-sectional data. Data collected at a given point in time. It asks for respondents’ age and then creates groups to look at the changes in wellbeing. It compares age based groups. The data does not look at the trends for an individual over time. The difference between such longitudinal studies and the cross-sectional findings is often profound. The same is the case here.
A longitudinal panel over many years captured wellbeing measures from each individual. Researchers realized that the sample changes with time. Illness takes its toll. People who are ill tend to have lower wellbeing. They are less likely to fill out the questionnaire. Wellbeing has being related to death. People with lower wellbeing drop out of the sample. The result is an in-built bias towards healthy individuals with higher well-being. The panel includes lots of other data about individuals. Researchers were able to “correct” for the biases.
This changes the pattern. Life satisfaction bounces back after the mid-life crisis. It then plateaus between the age of 65 and 75, After that it starts to decline. That decline accelerates into old age. As might be expected, life satisfaction is reduced by negative life events. The impact is significant. Being widowed or suffering a health shock can reduces satisfaction by about a third. Healthy ageing has pushed back these events but they have not gone away.
Apes and Man
The ape study described earlier is a cross-sectional study. It would be a massive undertaking to develop- longitudinal data. It would mean tracking individual apes over their entire life. At each age noting their apparent well-being. The study does show an apparent “midlife crisis”. There is a dip and a bounce. It did not describe the shape of the well-being/ life satisfaction curve later in life.
The source of the mid-life crisis is still mystery. It could be social or potentially biological. The well being paradox seems to be an artifact of the way the analysis was done. The good news ie that we do “come out” of the mid-life crisis. Our wellbeing increases until the age of 65. It then plateaus until the challenges of ageing arrive.
Love this! So much for all our hypotheses of midlife.
Would love pictures/ graphs of these curves and their source John. Can you share?