Dr Marina Davila Ross, from the University of Portsmouth and Professor Elke Zimmermann at the University of Veterinary Medicine in Hanover, Germany, studied the play behaviour of 25 orang-utans aged between two and 12 at four primate centres around the world.

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"When humans laugh, they voice stable sounds: that means the vocal folds are moving in a very regular synchronised way, " Dr Davila-Ross explained.

BBC: Tickled apes yield laughter clue

To put the idea on a firmer footing, Dr Davila-Ross made more than 800 recordings of the tickle-induced laughter of the apes and infants.

BBC: Tickled apes yield laughter clue

"There's a lot of research that has been going on, but this is the first study that has conducted the phylogenetic approach to measure these acoustics and relate them to one another, " Dr Davila-Ross.

BBC: Tickled apes yield laughter clue