Scientists have discovered that chimpanzees and orangutans can experience a mid-life crisis just like humans do.

A study of over 500 of the animals from around the world found their sense of well-being was highest in youth and old age but dipped in the middle.

The same U-shaped curve of happiness is seen in humans who appear most content early and late in their lives.

Scientists had adapted a questionnaire widely used to measure human well-being.

Biological factors

Zookeepers who knew the apes well were asked to rate their mood.

Both males and females appeared to suffer a drop in happiness at around the age of 40 to 50 in human years.

The results indicate that evolutionary and biological factors may play a part in a human mid-life crisis as well as economic events or social and cultural forces.

Lead researcher Prof. Andrew Oswald is from the University of Warwick in the UK.

"We hoped to understand a famous scientific puzzle: why does human happiness follow an approximate U-shape throughout life?" he said.

"We ended up showing that it cannot be because of mortgages, marital break-up, mobile phones, or any of the other paraphernalia of modern life" he added.