Scientific research shows great apes go through a midlife crisis just like homo sapiens.
The survey was conducted on 508 captive chimpanzees and orangutans who may well have been going through a whole-life crisis because they are in prison. Just a theory.
Contentment in life, for ape and man, can apparently be mapped as a U-shaped curve. Midlife crisis is the bit where you go round the bend.
Such a dip in chimpanzee happiness was first diagnosed during the making of the PG Tips adverts in the late 1970s. One of the chimp tea party stars protested that he was getting too old to wear red trousers and a silly hat just to sell teabags.
He was recast as a special agent, wearing a white tuxedo and saying: "The name's Bond. Brooke Bond." But the midlife crisis persisted and the chimpanzee closed the shop, sold the house, bought a ticket to the West Coast. Now he gives them a stand-up routine in Los Angeles.
Human behaviour, especially among males, includes buying sports cars, Harley-Davidson motorcycles, wearing unfeasibly bright clothes and embarking on ill-advised sexual adventures. The same is true of pandas. Like the one from Beijing who decided to spice up his life with a tattoo. He was told Edinburgh was the place to go and is now locked up in the local zoo. I know a panda is not an ape but bear with me.
There is evidence that midlife ennui does not apply to all great apes. Gorillas and bonobos appear to be immune. Gorillas just carry on getting grumpier as they get older.
This is borne out by my own study of Snowflake, the late and great albino gorilla at Barcelona Zoo.
He had to suffer an endless queue of humans with nothing better to do with their time. Snowflake's reaction was often to turn away and show his backside. Or pick and flick something interesting from a nostril.
Bonobos, the chimp-like great ape closest to homo sapiens on the evolutionary tree, maintain high levels of contentment.
They are always having sex and seem pretty happy at all ages.
They are a perfect role model for us humans. To go bonobo say: "I've got a terrible bout of midlife crisis. Any chance you can pop down this back close with me for a wee while?"