This is a wonderful blog post by one of my favourite bloggers, blag hag.
A simple discussion of what is actually natural when it comes to animal mating habits, and yes there isn't really anything that is natural or 'normal'. This is one of those arguments that really does annoy me on two fronts: first as the post shows there isn't any single mating habit that is natural. Second the naturalness of an action is a rubbish rationale to use with relation to humans, again as the post reports many animals eat their young, or their partners or carrion.
The naturalness of something is a stupid arguement and the sooner we move on from it the better. Either everything is natural (we are after all products of a natural environment) or we are better than that and it doesn't matter anyway. We certainly can't claim that some subset of our actions should be natural (sex etc) and another it doesn't matter (wearing skins of other animals).