November 20, 2012
Apes Have Mid-life Crises Suggesting Biological Link
redOrbit Staff & Wire Reports - Your Universe Online
Apes, like humans, experience a decline in happiness during middle age, which rebounds as they approach old age, according to a new study that suggests the infamous mid-life crisis may have biological, rather than sociological, roots.
Humans across many cultures report a dip in happiness during their late-40s when compared with their life satisfaction during younger and older years.
In the current study, an international team of researchers studied 508 great apes in captivity, and found that the animals´ sense of well being bottomed out during their late 20s to mid-30s -- the ape equivalent of middle age -- before recovering in old age.
"There's a common understanding that there's a dip in wellbeing in middle age, and that's been found in many datasets across human cultures," said study leader Alex Weiss, a psychologist at Edinburgh University, during an interview with The Guardian.
"We took a step back and asked whether it's 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.”
The findings suggest that the midlife crisis may have its roots in the biology humans share with our nearest evolutionary cousins.
The researchers asked zookeepers, caregivers and others who worked with 508 male and female chimpanzees and orangutans of various ages to complete questionnaires about the animals.
The apes included two separate groups of chimpanzees, and a group of orangutans from Sumatra or Borneo. All resided in zoos, sanctuaries and research centers across the U.S., Australia, Japan, Canada and Singapore.
The survey included queries about each animal's mood, their pleasure when socializing and their success at achieving certain goals.
The researchers also asked the caregivers to describe how they would feel about being the ape for a week.
The responses were scored from one to seven.
The researchers analyzed the caregivers´ responses, and found that wellbeing in the apes dropped during middle age, but rose again as the animals moved into old age.
The peak wellbeing occurred, on average, at 28.3 and 27.2 years old for the chimpanzees, and 35.4 years old for the orangutans. Considering that great apes often live to 50 or more during captivity, these ages correspond to middle age.
"In all three groups we find evidence that wellbeing is lowest in chimpanzees and orangutans at an age that roughly corresponds to midlife in humans," Weiss said.
"On average, wellbeing scores are lowest when animals are around 30 years old."
The researchers said the temporary fall in ape wellbeing could be the result of depressed apes dying younger, or of age-related changes in the brain that are also present in humans.
Weiss noted that the similarities between humans, chimps and orangutans go beyond genetics and physiology, and said he believes the findings could provide a deeper understanding of the emotional crisis some humans experience during middle age.
"If we want to find the answer as to what's going on with the midlife crisis, we should look at what is similar in middle-aged humans, chimps and orangutans," he said.
Humans and apes face similar social pressures and stress factors, he added.
"You don't have the chimpanzee hitting mid-life and suddenly they want a bright red sports car, but there may be other things that they want like mating with more females or gaining access to more resources,” he told BBC Nature.
But other scientists are skeptical about the findings.
"What can produce a sense of wellbeing or contentedness that varies across the lifespan like this? It's hard to see anything in an ape's life that would have that sort of pattern, that they would cogitate about,” said Robin Dunbar, professor of evolutionary psychology at Oxford University, during an interview with The Guardian.
“They're not particularly good at seeing far ahead into the future, that's one of the big differences between them and us."
Psychology professor Alexandra Freund at the University of Zurich also found the study´s findings dubious, saying that the concept of a midlife crisis was questionable even in humans.
"In my reading of the literature, there is no evidence for the midlife crisis. If there's any indication of decline in emotional or subjective wellbeing it is very small and in many studies, it's not there at all,” she said.
But study co-author Andrew Oswald, an economics professor at the University of Warwick who has researched human happiness for 20 years, says the phenomenon is authentic.
“The mid-life crisis is real and it exists in...our closest biological relatives, suggesting that it is probably explained by biology and physiology,” he said.
"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,” he told BBC.
It was "quite mind-blowing... to find it in apes,” he said.
“Maybe evolution needed us to be at our most dissatisfied in midlife,” he said.
Weiss said the study provides interesting opportunities for future research, since the mid-life crisis has long been thought to be specific to human society.
"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."
The study was published online on Monday in the journal Proceedings of the National Academy of Sciences (PNAS).