Redundancy in nature?

Nature is mindblowing! Everything is so extremely complex, and yet perfect. There are no mistakes...or are there?

I have been hard-pressed to find elements in nature that are completely redundant. (just a thought that crept into my mind) My list is short, but this one has been bugging me for a long time:

Why do men have nipples?

The link takes you to a book I saw on Amazon - Looks like a worthy read. Do you know of any other perceived redundancies in nature? Feel free to enlighten me...