Do you know a chimp who's feeling doleful? Mid-life crisis, probably

Boffins investigating the feelings of hundreds of chimpanzees, orangutans and varied great apes say that the creatures get depressed in their middle years just as humans - perhaps especially human males - do. They consider that this affirms Charles Darwin's famous dictum to the effect that if we would seek to understand ourselves we would do well to have a think about baboons first.

"We hoped to understand a famous scientific puzzle: why does human happiness follow an approximate U-shape through life?" explains Professor Andrew Oswald of Warwick uni. "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 those."

Oswald and his colleagues found this out by evaluating the cheeriness of some 508 simians living in zoos around the world "whose well-being was assessed by raters familiar with the individual apes". They found that just as with humans, apes start out in life feeling pretty good about things. Then they hit middle age, and start doing the chimp or orangutan equivalent of spaffing the kids' college fund on a sports car or running off with the receptionist.

But chimps who live to a ripe old age, just as with humans, gradually climb out of the pit of despair and start feeling rather cheery again (until shortly before death, that is).

The investigating boffins acknowledge the possibility that it might just be that cheerfulness makes you live longer, so that only naturally cheery apes survive to get old (this would be less the case among people - from wealthy nations at least - as death before old age is quite rare for them). The scientists write:

Higher rates of mortality for the least happy apes, especially in later life, could account for part of the higher wellbeing in the older ape populations.

However they also consider that there are likely to be other explanations, perhaps applying to both humans and apes, which would account for the U-shaped cheeriness curve with age. Probing these, they consider, might not only lead to less dolefulness in the ape house at the zoo: it could also one day eliminate such social scourges as 50-year-old men on powerful motorbikes, practicing on electric guitars, absconding with waitresses etc.

As the boffins note, back in 1838 famed brainbox Charles Darwin - about to commence the research which would prove our common ancestry with the apes - jotted in his notebook:

Origin of man now proved … He who understands baboon would do more towards metaphysics than Locke. [John Locke, the great 17th-century Enlightenment thinker generally said to have had much to do with forming many modern ideas on how people should get on with one another such as the social contract, religious tolerance etc].

The ape investigators write that their proposed simian mid-life crisis mechanisms, perhaps also at work in humans, "offer applications beyond the midlife nadir in happiness and could affirm Darwin’s view".

Their paper can be read in full for free here in pdf, courtesy of the Proceedings of the National Academy of Sciences. ®