It is innate within humans to want to live (extremely rare exceptions a given). This innate desire to live is self evident. The self evidence of this desire can only be logically expressed in a right to life. In this way, a right to life is a natural right.
Is it logical to presume that ones innate desire is also innate in others? Yes. Is it possible to confirm this? Yes. Is it reasonable to construe this innate desire as a natural right? Yes. Is this natural right logical and reasonable? Yes.
While all rights can (even justly) be taken away or refused, they do represent morality and, in this particular case, I've clearly explained how the morality is both logical and reasonable.