Darwin's theory of evolution tells us that natural selection favours traits that give their organism an advantage over others of it's kind or predators it may encounter. Sure, there are cases where a certain trait appears illogical and even decreases the chances of survival for a species but most of them (like the disposition of female Peacocks to select males with more impressive tail feathers) can be linked in to sexual selection and is explained as a way for animals to strive for "better" genes passed to their offspring.
The sensation of being tickled doesn't conform to either natural or sexual selection. In fact, it's a disability and possible danger for an animal to have a tickle reflex since when you get going it positively immobilises you on the spot and prevents you from fighting or fleeing which would suggest that animals without this reflex would have an advantage, however slight, over one that does have it. Obviously when a lioness is bounding after you it's not to have a quick tickle at your ribs but it would still be a disadvantage in some scenarios I'm sure.
We also don't select a mate dependant on whether or not they appreciate a good tickle and there's no way of telling if a person is ticklish just by looking at them so it clearly has nothing to do with sexual selection.
For me, this falls under the same kind of heading as why we appreciate music, in Daniel C. Dennett's book Breaking the Spell he suggests that we have evolved to lose ourselves in certain beats, rhythms and melodies as a way of coping with and easing stress and he argues that in our more primitive past religion possibly had the same effect and so it was of evolutionary benefit to us. Just like our appreciation of music (tried really hard to find a decent video of a parrot that's clearly moving to a beat but failed
), it's also not something that is exclusive to humanityCould tickling have had the same benefit in our past or is it possibly something that we have developed more recently in our history with the onset of society and the relative saftey it provides us as a species meaning things that would have set us back, like being immobilised by touching certain parts of out skin, have more of a chance to develope since they don't pose enough of a threat to significantly decrease our chances of survival?
If the sensation only manifested itself when you get your feet tickled then I could understand this trait a bit more since looking at the way our brain works shows that the parts that deal with sensory perception of your feet are right beside those that register the perception of your genitals (represented by a Sensory Homunculus below) and so some sort of neural cross firing or synethsesia could be the cause of it. When you think about it, the feeling you get while being tickled isn't too dissimilar to the feeling you get when you orgasm all be it on a much smaller scale which is probably what made me think of the connection between sensory regions in the brain in the first place (coupled with the fact that feet are often the most suseptable to being tickled)
Wikipedia clases being tickled in two different ways:
knismesis (light tickling)
and gargalesis (heavy tickling)Wikipedia wrote:Knismesis refers to the light, feather-like type of tickling. This type of tickling generally does not induce laughter and is often accompanied by an itching sensation.[2] The knismesis phenomenon requires low levels of stimulation to sensitive parts of the body, and can be triggered by a light touch or by a light electrical current. Knismesis can also be triggered by crawling insects or parasites, prompting scratching or rubbing at the ticklish spot, thereby removing the pest. It is possible that this function explains why knismesis produces a similar response in many different kinds of animals.[2] In a famous example, described in Peter Benchley's Shark!, it is possible to tickle the area just under the snout of a great white shark, putting it into a near-hypnotic trance.[3]
From those articles there's another possible evolutionary advantage to being lightly tickled, I.e, in order to tell that something possibly dangerous is maybe crawling on your skin, the itchy feeling that accompanies it could be a reflex action designed purely to get whatever is on you away from your body since your hand will brush the spot that itches instinctively.Wikipedia wrote:Gargalesis refers to harder, laughter-inducing tickling, and involves the repeated application of high pressure to sensitive areas.[2] This "heavy tickle" is often associated with play and laughter. The gargalesis type of tickle works on humans and primates, and possibly on other species.[4] Because the nerves involved in transmitting "light" touch and itch differ from those nerves that transmit "heavy" touch, pressure and vibration, it is possible that the difference in sensations produced by the two types of tickle are due to the relative proportion of itch sensation versus touch sensation.[5]
While it is possible to trigger a knismesis response in oneself, it is usually impossible to produce gargalesthesia, the gargalesis tickle response, in oneself.[2]
Hypergargalesthesia is the condition of extreme sensitivity to tickling. [6]
Reading more from Wikipedia there is actually a bit about what Darwin apparently thought about the reaction:
A good point but I don't think it answers the effect as fully as it should,Wikipedia wrote:Charles Darwin theorized on the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure.[9] If a stranger tickles a child without any preliminaries, catching the child by surprise, the likely result will be not laughter but withdrawal and displeasure. Darwin also noticed that for tickling to be effective, you must not know the precise point of stimulation in advance, and reasoned that this is why you cannot effectively tickle yourself.
If you want to read the full article then the link is HERE
(I know it has a practical use but why the hell does it feel so good?)
(Or did I miss your point?)