Shades of Eden

http://www.livescience.com/animalworld/060721_snake_primate.html

According to a biologist, early human development was shaped by our struggles against snakes.

This is a cool idea. It makes sense, and it lets you put an interesting spin on a famous story from Genesis 3 (in accord with my noted habit for interpreting the Bible in a way most guaranteed to drive the religious right bonkers).