Hmmmm.... Eeenteresting. I guess i'll try and elaborate on the points tkpatience made.
welledy welledy welledy... Well, we do like to laugh yes? If we are male and straight, seeing a woman laugh with genuine pleasure or amusement is generally a clear cut sign that she wants you to keep paying attention to her. Hearing laughter is instictually pleasing to us; its inherent in a human's social communicative repetoire. Studies done on tribes in south america and other parts who had previously had almost no contect with the modern world, showed that a big grin meant to them the same thing it does to us: enjoyment. So, safe to say, one reason we all enjoy tickling people to one degree or another is because, at a basic level, we like hearing people laugh.
Also, because we are 'social animals' if you like, dominance and submissiveness are inherent in our blood; all humans societies have hierarchies of one form or another. Thus for many, even if they're not fetishists, a buzz is got from feeling 'higher up in the chain'. The proportion of dominant males and females in sexual fetishes, and in general positions in society, suggests that being 'dominating' is more instinctually appealing (in general) to men, and that women find, once again not exclusively but in a general trend, more pleasure from the reverse role. But that's a bit of a tangent. Point is, if your stronger than someone, have greater strength in numbers (getting someone else to hold the lee down etc), have mechanical power over them (chains, ropes, bonds... although this one is more exclusive to the fetishists, in the case of tickling) and so on, and are able to control them, and in the case of tickling often have them ask you to stop, it gives an instictual, buzzing sense of being the master, even if your not consciously aware of the 'dominant-submissive' relationship. Hence another reason why many non fetishists enjoy tickling; it empowers.
Phew. Lets see.... anything else... Well, we all do like to touch each other. It gives us a feeling of connection. Even straight men seem to genuinely enjoy touching one another, in spite of the homosexual prejudices inherent in our modern world, as is shown by their behaviour when drunk, when said social walls are less restraining (lots of hugging, patting, hand to hand contact etc.) and also from examples of less homophobic societies, like ancient greece or rome, or even modern europe where straight men often kiss without thinking anything of it. This implies that we instictually just *like* human touch, regardless of what gender or orientation its from. This could be another reason why we enjoy tickling; we take pleasure from being in friendly physical contact with any other person, without anything sexual necessarily being implied.
There may of course be something chemical involved, in terms of hormones and such, but that is not an area in which I am magnificently knoledgeable, so I'll steer well clear. Anyhoo, hope that was helpful.
See ya.
