Sure, there's a difference between the two. While I don't feel qualified to put forth my own definitions of the two, I can give examples of how to tell which is which.

Example: Nail biting. Definitely habit, not nature, because it is not a response normally exhibited by humans as a race.

How to determine nature? The best test would likely be to put various people from different societies into situations, and see if there is a common reaction to them. For example, if an American responded to a situation with a similar reaction as, say, a Kalahari bushman, then we're probably seeing an example of human nature.

There, you now have my feeble attempt at a reply. Carry on.