We’ve all been there. The trees we enjoyed climbing as kids no longer beckon quite so beguilingly. The fruits and nuts that were such delicious treats have largely lost their appeal. If we’re honest with ourselves, we are forced to admit: We’re in something of a mid-life crisis.
Yes, getting older can feel oppressive to an orangutan.
We can now add the middle-age blues to the list of experiences we mistakenly thought were exclusive to humans. In a paper just published in the Proceedings of the National Academy of Sciences, an international research team reports the well-being of great apes apparently follows the same curved pattern familiar to homo sapiens, reaching its low point in midlife—that’s around age 30 for these creatures—and then rebounding as they move into late adulthood.
“We hoped to understand a famous scientific puzzle: why does human happiness follow an approximate U-shape through life?” said University of Warwick economist Andrew Oswald, one of the paper’s five authors. “We ended up showing that it cannot be because of mortgages, marital breakup, mobile phones, or any of the other paraphernalia of modern life. Apes also have a pronounced midlife low, and they have none of these.”
The researchers, from three continents, looked at 508 great apes: 155 chimpanzees from Japanese zoos, research centers and a sanctuary; 181 chimpanzees housed in U.S. and Australian zoos; and 172 orangutans housed in zoos in the U.S., Canada, Australia and Singapore. Caretakers who knew the animals well (usually for at least two years), including zookeepers and researchers, assessed their well-being using four measurements.
They rated whether the great ape was generally in a positive or negative mood; how much pleasure he or she seemed to derive from social situations; and how successful he or she was in achieving goals. Finally, the caretakers were asked “to indicate how happy they would be if they were the subject for a week.”
The patterns that emerged were pretty much identical for the three samples. The youngest great apes scored the highest in terms of overall well-being. Those in middle-age had the lowest scores, while the older animals were, on average, reasonably content.
“Our results imply that human well-being’s curved shape is not uniquely human, and that, while it may be partly explained by aspects of human life and society, its origins may lie partly in the biology we share with closely related great apes,” concludes the research team, which was led by University of Edinburgh psychologist Alexander Weiss.
The researchers speculate that, like humans, “the least happy apes” could have higher rates of mortality, which may account for the upward happiness curve for those who survive into later life. “A second possibility is that the U-shape arises in humans, chimpanzees and orangutans via similar age-related changes in brain structures,” they write.
“Finally, older adults in all three species may rely on behavioral mechanisms to regulate their emotions,” the researchers add. “For example, they may seek out situations and group members that elicit more positive emotions, or shift to goals that are more attainable in older age.”
Yeah, to hell with those youngsters romping around at the top of that tree. I’m literally going with the low-hanging fruit, and I plan to enjoy it.
It’s worth reiterating that these were not observations of great apes in the wild. It’s possible that the animals’ midlife depressions reflected the conditions of their captivity.
It’s also worth considering that their caretakers may have been, at least in part, projecting their own feelings onto the animals. Whether a chimpanzee achieves his or her goals is a rather subjective analysis.
Nevertheless, this apparent commonality is intriguing and may shed light on the biological underpinnings of our own emotional trajectories. What’s more, pharmaceutical companies will be enticed by the notion of a new market for their products.
Surely we won’t have to wait long before the introduction of primate Prozac.