What is the purpose of tickling?

Stop it, I love it

Also in this week's column:

• Why do your hands turn white when you wash the dishes?
• Why do you sometimes shiver when you wee?
• What is a confessing Sam?

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

• It is unknown why certain areas of the body are more ticklish than others.
• Men and women are just as "ticklish". But a few studies suggest that, if either, men may be slightly more ticklish than women.
• You cannot tickle yourself. If you try, you will not succeed since there is no surprise or lack of control in the stimulation. But a few studies dispute this as well.
• 85 per cent of adults in some way or another enjoy being tickled, tickling others, or watching others being tickled.
• Tickling was used as a torture by the ancient Romans.
• Tickling is used in sexual fetishism where it is known as "tickle torture".
• Research by Dr Sarah-Jayne Blakemore of the Institute of Cognitive Neuroscience in London found that robotic arms used to tickle people are just as effective as human arms.
• Research by Dr D S Bennett of the Integrative Treatment Centres in Denver established that the tickling response is well established by four months of age.
• Research headed by Dr M Blagrove from the University of Wales in Swansea shows that the normal tickling response may be absent in those with schizophrenia.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to [e-mail]