What is the philosophical justification for the right to life?

I am not trying to directly frame this issue as part of the abortion debate, but I would like to know what philosophers have said about how the right to life is justified. I have a generally libertarian stance, with a strong emphasis on personal property rights (Locke). However, I see a lot of problems in justifying life by itself as a right. What constitutes 'life' in this sense? Plants are alive, but obviously do not have a right to life. I see a contradiction between property rights and a right to life. For example, human beings would not require food, shelter, clothes, etc. if they did not have a right to life. But as stated before, if you subscribe to a philosophy of strong property rights, then individuals have no inherent right to food, shelter, clothes, unless they acquire them of their own accord. For me, the right to life is so vague that I don't see how it can be reconciled against other rights.<br><br>If anyone can point me to a philosopher (or philosophers) who has written extensively about this issue, I'd greatly appreciate it.<br><br>EDIT: Thank you for the responses so far. I am reading through Locke's second treatise, and Hobbes' Leviathan, and some of Kant's political writings on rights. I appreciate the advice for more Hobbes and Rawls. Much appreciated.