Normally when one mentions the “natural rights” of man, people think you are trying to slip God in the back door. Why? I don’t know, it was the non-observant Jewish libertarian Murray Rothbard who used “natural rights” as a base to his Rothbardian System. I don’t think one can accuse him of trying to slip God in the back door; even if he was married to a nice Roman Catholic girl. See his “Introduction to Natural Law” at the Mises Institute here.
Natural law and natural rights follow from the nature of man and the environment he finds himself in. Due to our circumstances we have the right to defend ourselves and our property. This leads to true natural law which is not derived from some kingly law giver or the horrible power of a State.
Utilitarian and relativist philosophers demand that advocates of natural law use a definition of natural law that is independent of man’s nature or his environment. This is trying to win an argument by hostile definitions; clever buy logically flawed. Natural Law comes from man’s natural rights which comes from man’s nature and circumstances.
Natural law follows from evolutionary theory since the use of force for defence is natural for humans and similar animals. Our capability to make moral judgements has evolutionary benefits, else the trait would not have come to be. In other words, the capacity to know good and evil, has immediate evolutionary benefits.
As Rothbard wrote in the above referenced essay:
Among intellectuals who consider themselves “scientific,” the phrase “the nature of man” is apt to have the effect of a red flag on a bull. “Man has no nature!” is the modern rallying cry and typical of the sentiment of political philosophers today was the assertion of a distinguished political theorist some years ago before a meeting of the American Political Science Association that “man’s nature” is a purely theological concept that must be dismissed from any scientific discussion.
In the controversy over man’s nature, and over the broader and more controversial concept of “natural law,” both sides have repeatedly proclaimed that natural law and theology are inextricably intertwined. As a result, many champions of natural law, in scientific or philosophic circles, have gravely weakened their case by implying that rational, philosophical methods alone cannot establish such law: that theological faith is necessary to maintain the concept. On the other hand, the opponents of natural law have gleefully agreed; since faith in the supernatural is deemed necessary to belief in natural law, the latter concept must be tossed out of scientific, secular discourse, and be consigned to the arcane sphere of the divine studies. In consequence, the idea of a natural law founded on reason and rational inquiry has been virtually lost.
Natural Law (Libertarian law) as well as “human rights” rests on a foundation of the inalienable rights of man that come with his birth and not as a gift from his rulers. We must educate ourselves on the non-religious foundation of human rights via reason and logic as Rothbard and so many others have done. Don’t let the Utilitarians fool you into believing otherwise, since at its heart liberty must be defended on moral and ethical grounds as well as other grounds. Natural Rights is the heart of the moral defense.