Some of you may remember my two posts on the nature of rights in 2008. If so, you can now forget them, because David Friedman has made the argument more completely and much more eloquently.
Rights in human societies, including modern ones, are based on the same pattern of behavior as territorial behavior in animals or enforcement via feud and the threat of feud, even if less obviously so. Each individual has a view of his entitlements and is willing to bear unreasonably large costs in defense of them.
Yup, that's what rights are.