Subject: Why do humans have fetishisms as a part of their their sexual behaviour?

My mind sometimes boggles by the sexual preferences human beings get into. 
Almost anything can be a turn on for any given person. What physical, 
psycologiocal and/or social mechanisms turns a persons sexuality towards 
any specific fetish? Are we somehow predisposed to specialise our sexual 
behaviour, or could extreme fetishism be said to be at odds with nature, 
where sexuality ultimately is a tool for reproduction? I do not with this 
try to say that fetishists are abnormal in any way, or that there is only 
one acceptable sexuality, but I would like to know if there is any 
scientific explanation on what makes some people aroused by teddy bears. 
And lingerie. And rubber. And so on.  

Re: Why do humans have fetishisms as a part of their their sexual behaviour?