Darwin had began to test his theory about expression in 1867 by gathering information on emotional behaviour through a questionnaire, originally hand-written and later printed, which he sent to a variety of correspondents around the world ; Darwin’s questionnaire included questions on laughter and other expression of mirth, as first seen in his letter to F.J.H von Mueller in 1867:
Darwin wanted to show that most expressions are innate in humans and that shared expressions are evidence of common descent not just of all human races, but of humans and other animals.
As mentioned in our previous post, Darwin wrote in The Expression of the Emotions in Man and Animals (1872) that “If a young chimpanzee be tickled—and the armpits are particularly sensitive to tickling, as in the case of our children,—a more decided chuckling or laughing sound is uttered; though the laughter is sometimes noiseless. “[Expressions page 132]
Darwin’s readers at the time could only imagine the scene, whichg Darwin’s description made very vivid… Well, for us, it is actually possible to see baby monkeys being tickled and hear their laugh!
When in 2009, scientists studied human laughter, the BBC reported the piece of news by illustrating it with a video of a ticklish young orangutan (The scientists’ conclusion was that human laughter can be traced back to 10 to 16 million years ago). You will surely smile when seeing this ticklish baby!