There comes a time in some men's lives when the days seem darker and the only sensible response is to blow their life savings on a sports car.
Radical and often ill-advised changes in lifestyle have become the calling cards of the midlife crisis, but if it is more than a myth, then humans may not be the only animals to experience it.
An international team of scientists claims to have found evidence of a slump in wellbeing among middle-aged chimpanzees and orangutans. The lull in happiness in the middle years, they say, is the great-ape equivalent of the midlife crisis.
The study, which was published in the journal Proceedings of the National Academy of Sciences, has raised eyebrows among some scientists. But, according to the authors, the findings suggest that the midlife crisis may have its roots in the biology humans share with our closest evolutionary cousins.
"There is a common understanding that there is a dip in wellbeing in middle age and that has been found in many data sets across human culture," said Alex Weiss, a psychologist at Edinburgh University.
"We took a step back and asked whether it is possible that, instead of the midlife crisis being human-specific and driven only by social factors, it reflects some evolved tendency for middle-aged individuals to have lower wellbeing," he said.
The team from the United States, Japan, Germany and the United Kingdom asked zookeepers, carers and others who worked with male and female apes of various ages to complete questionnaires about the animals. The forms included questions about each ape's mood, the enjoyment they gained from socialising and their success at achieving certain goals. The final question asked how carers would feel about being the ape for a week. They scored their answers from one to seven.
More than 500 apes were included in the study in three separate groups. The first two groups were chimpanzees and the third was made up of orangutans from Sumatra or Borneo. The animals came from zoos, sanctuaries and research centres in the US, Australia, Japan, Canada and Singapore.
When the researchers analysed the questionnaires, they found that a sense of wellbeing in the apes fell in middle age and climbed again as the animals moved into old age.
In captivity, great apes often live to 50 or more. The nadir in the animals' wellbeing occurred, on average, at 28.3 and 27.2 years old for the two groups of chimpanzees and 35.4 years old for the orangutans. "In all three groups, we find evidence that wellbeing is lowest at an age that roughly corresponds to midlife in humans," Weiss said.
But Weiss conceded that apes are not known to pursue radical and often disastrous lifestyle changes in middle age. – © Guardian News & Media 2012