Where does Natural Law come from?

"Is it possible that there is no Natural Law and man can know moral order and unalienable rights from his own reasoning, unaided by the supernatural or God? There are, of course, those who argue this case--including the atheist and others who attempt to distinguish Natural Law from Divine Providence. It is not the view adopted by the founders of America. This position would, it seems, lead man to arbitrarily create his own morality and rights--right and wrong, just and unjust, good and bad, would be relative concepts susceptible to circumstantial applications. Moreover, by what justification would 'Life, Liberty, and the pursuit of Happiness' be 'unalienable Rights' if there is no Natural Law, since reason alone cannot make them inviolable? What then is Natural Law if its origin is unknown or rejected? it is nothing more than a human construct. An individual may benefit from the moral order and unalienable rights around which society functions while rejecting their Divine origin. But the civil society cannot organize itself that way. It would become unstable and vulnerable to anarchy and tyranny, imperiling all whthin it, especially the individual. The abandonment of Natural Law is the adoption of tyranny in one form or another, because there is no humane or benevolent alternative to Natural Law." Mark Levin Liberty and Tyranny 2009 Page 26.