As science experiments go, it was real hoot.
Researchers mapping the evolution of laughter gently tickled the feet, palms, necks and armpits of baby humans and apes.
By analysing the sounds the animals made - giggles, hoots, grunts and pants - they concluded that laughter can be traced back some 16million years, and that it evolved along the same pathway as our evolution.
In the first study of its kind, Portsmouth University researchers tickled three human babies and young orangutans, gorillas, chimps and bonobos and recorded their 'laughter'.
They then teased apart the different sounds in the recordings and mapped the similarities between animals. The result looked like the evolutionary family tree, in which humans are most closely related to chimps and bonobos and most distanced from orangutans.
And it showed that laughter evolved gradually over the last 10million to 16million years, reports the journal Current Biology.
Primatologist Dr Davila Ross said: 'Our results on laughter indicate its pre-human basis.
'This is important for emotional research in humans and animals as well as for the management of primates in captivity and in the wild.'
The analysis also revealed that gorillas and bonobos have some control over their breathing - a skill that was thought to be unique to humans and to have played an important role in the evolution of speech.
Dr Ross said that apes use laughter differently to humans, adding: 'Although we can use it to mock each other, previous research has indicated it developed in our ancestors as a play tool.
'Apes like to play with each other and sometimes this can get out of hand so their form of laughter is used to prevent them getting over aggressive.'
Jaak Panksepp, a scientist from Washington State University in the U.S. who studies laughter-like responses in animals, said the findings were exciting.
His work has suggested that even rats 'laugh' in response to play and tickling - producing chirps too high-pitched for people to hear.
Other studies have shown that young chimps can outperform people in memory games, completing them more quickly and with fewer mistakes.
Scientists have also observed chimpanzees making a 'toolbox' of items when foraging for food and gorillas using branches to test the depth of water they plan to wade
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