This is just my personal opinion, but I don't think humans are born with a "natural" fear of anything. Be it snakes, heights, spiders, close-in spaces, clowns, or anything else. I think all those deep-seated fears are brought on by something. It may be something that happened so early on that the person has no recollection of it. It may be something that happened extremely gradually (societal influences) so that no specific root cause can be identified....but none of it is "born" into us.