What the Heck is Tickling About Anyway?

Over at the very interesting Conscious Entities is a post about emotions, which got me thinking about tickling (see the comments). First off, an extract from an article on tickling from the Register:

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.

I don't know how sold I am on the idea that tickling is conducive to forming social bonds. I've had a few girlfriends who would threaten very severe punishments for even thinking about tickling them. Some more from an interesting (if not slightly old) article on tickling, from the Telegraph:

However, the work does change the nature of a long-running debate over one ticklish conundrum that has split scientists for more than a century: the cause of our merriment. Some say that the chuckle induced by a tickle is a reflex. Others argue that it is the result of close physical contact with another person, and thus "socially induced", an idea put forward by Charles Darwin in 1872. The inability to tickle oneself had been thought to support Darwin's theory. However, the new work shows tickle-induced laughter is indeed a reflex, one that can only work in social situations, say, when a friend is brushing a feather against the sole of your foot.

There remains one deeper question. Why do we laugh? The psychologist Wallace Chafe put forward the idea that laughter serves to incapacitate us, acting as a disabling device that allows you to relax when you realise that a threat is not genuine.

In his new book, Phantoms in the Brain (Fourth Estate), Prof Vilayanur Ramachandran of the University of California says that this idea, though intriguing, does not explain our need to generate "rhythmic, loud explosive sounds". We chortle to tell other people that a perceived threat or anomaly is trivial. "You approach a child, hand out menacingly . . . But no, your fingers make light, intermittent contact with her belly," he writes. "As a result of this tickle, the child laughs, as if to inform other children, 'He doesn't mean harm'."

And in the end, I really haven't got a good idea what the answer to tickling actually is. Perhaps it's just a quirk of evolution, one of those occasions when the reflex elicits a not very sensible reaction (and here I'm thinking of the feeling you get when you hit your funny bone - which I presume you can do yourself?).