One thing I have enjoyed since leaving the Jehovah's witnesses is learning about science and evolution. It's so great to be able to look at things without the fog of religious belief clouding things. Of course I have learned a lot from Cofty and his threads on evolution, but one thing I struggled with was what causes instinctual behavior in animals For example, what tells birds to fly south for the winter? Obviously there isn't a "fly south for the winter" gene per se, so how do birds know to do that? I think Cofty tried to explain it to me once, but I just didn't get it.
So I came across this article from Nova which I think explains it pretty well for us non scientific types.