Original URL: http://www.theregister.co.uk/2006/09/01/the_odd_body_tickling/

What is the purpose of tickling?

Stop it, I love it

By Stephen Juan

Posted in Science, 1st September 2006 14:19 GMT

Also in this week's column:

What is the purpose of tickling?

Asked by Lou Portman of Los Altos, California, USA

As every child knows, tickling is the act of touching a part of the body so as to cause involuntary laughter.

The subject of tickling has intrigued philosophers since antiquity. Even Plato and Aristotle speculated about tickling and its purpose.

"Tickle" is derived from the Old English word tinclian meaning "to touch lightly".

None other than Charles Darwin was the first scientist to seriously analyse this most peculiar human behaviour. In The Expression of the Emotions in Man and Animals (1872) Darwin described in detail the involuntary spasms tickling triggers in babies, children, adults, and non-human primates. He concluded that tickling was an ingredient in forming and keeping social bonds. Such bonding occurs through stimulating each other to laugh and feel merry. This is particularly true for parents and children.

Darwin noted that the key to success in tickling is that "the precise point to be tickled must not be known" to the person being tickled. Thus, it is surprise rather than tactile pressure that is a key ingredient in tickling.

Subsequent laboratory experiments have found that in people who are extremely suggestible, the threat of being tickled without laying a finger on them is enough to induce hysterics. This is as effective with adults as with children and provides a clue to the fact that tickling is not merely a physical sensation as Darwin theorised.

Apart from Darwin's social bond theory for the importance of tickling, there is a simpler theory. The sensation felt when being tickled is similar to the one felt when insects crawl on the body. The tickle response may be a protective warning device against the stings and bites of harmful insects.

Interesting facts

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au