The nature and origin of rights isn't something that most people spend much time thinking about — it's usually a subject for political and legal philosophy.
It is important to the average person, though, because unless we have some idea about where rights come from, we can't say what is and is not a right — much less defend rights against the attacks of those who are more authoritarian.
In Shouting Fire: Civil Liberties in a Turbulent Age, Alan Dershowitz writes:
Rights do not come from God, because God does not speak to human beings in a singular voice, and rights should exist even if there is no God.
Rights do not come from nature, because nature is value neutral.
Rights do not come from logic, because there is little consensus about the a priori premises from which rights may be deduced.
Rights do not come from the law alone, because if they did, there would be no basis on which to judge a given legal system.
Rights come from human experience, particularly experience with injustice. We learn from the mistakes of history that a rights-based system and certain fundamental rights — such as freedom of expression, freedom of and from religion, equal protection of the laws, due process, and participatory democracy — are essential to avoid repetition of the grievous injustices of the past. Working from the bottom up, from our experiences with perfect injustice, rather than from the top down, from a theory of perfect justice, we build right on a foundation of trial and error.
In a word, rights come from wrongs.
It should be noted that Dershowitz, an orthodox Jew and obviously a believer in the existence of God, states right in his first point that rights do not come from God. He believes in God, but is clear that rights do not come from God. This contradicts what many in the Christian Right say, but it may make sense from a Jewish perspective.
After all, there is nothing in the Jewish scriptures about God preferring any particular system of government. God is recorded as setting forth basic moral principles, but no political principles. This is also the case when it comes to the Christian scriptures, but perhaps this isn't something that enough Christians have figured out yet.
[M]y theory of rights is really a theory of wrongs. It begins with what experience has shown to be absolute injustices: the Crusades, the Inquisition, slavery, the Stalinist starvation and purges, the Holocaust, the Cambodian slaughter, and other unquestionable abuses. It then asks whether the absences of certain rights contributed to these abuses.
If so, that experience provides a powerful argument for why these rights should become entrenched. The bottom-up approach builds on the reality that there is far more consensus about what constitutes perfect injustice than about what constitutes perfect justice. If there can be agreement that certain rights are essential to reduce the chances of perfect injustice, that constitutes the beginning of a solid theory of rights.
Dershowitz's idea of rights, briefly quoted here, is one that I find interesting. Instead of proceeding from a positive conception of rights, he proceeds from a negative conception of what has been "wrong" in the human experience. Instead of looking to what positive things rights are supposed to achieve, he first looks to what negative things rights might be expected to avoid.
At first, this may sound pessimistic, but it does have an important advantage: there are tremendous disagreements among political theorists about what rights are supposed to achieve, but there is far less disagreement about what qualifies as tremendous wrongs that we should want to avoid. Put more specifically, there is little disagreement that things like the Holocaust and the Stalinist purges were horribly wrong.
Thus, if nothing else, Dershowitz's theory of rights at least could provide a unified basis from which theorists of many different perspectives and beliefs can begin. People may end up in different places, it is true, but if they start out from the same position there may be greater opportunities for agreement down the road.
I believe, though, that Dershowitz's ideas about rights have more than just this pragmatic value. I believe that the political conception of "rights," basic liberties that the government has a positive obligation to defend, honor, and support, grew out of people's desire to avoid injustices. Perhaps the earliest moves towards rights were not against "absolute" injustices, but they were injustices nonetheless.
If a government is going to be just, and one which upholds justice, then it must fight injustice. Sometimes, injustice is best countered by establishing a sphere of rights which cannot be breached. We may not always know where and when such spheres of rights should be created, but we can develop a good idea about it by looking at the worst injustices and determining how right might have helped prevent them — just what Dershowitz recommends.
Conceiving of rights as immutable, eternal creations of some alien deity would not easily ahcieve the same ends. After all, such rights cannot be modified or amended based on new experiences of new wrongs. Even worse, they might be abused in a way that leads to mew wrongs. Defenders of the idea that rights have a divine origin treat the ability to amend or modify rights as a weakness; it's true that this does come with potential danger, it is also necessary for great benefits.