While I do question the origin (like Njorl), I take a much more scientific approach: rights are principles that when applied to a society result in peace, stability, prosperity, happiness, etc. Simply put, they are what
works.
Slightly differently from Njorl, I believe rights are inalienable not because they were handed down by God (they could have been, but I don't really know), but because we have
defined them to be.
The specifics of rights are the same as any other theory: you tweak the theory until the results match the hypothesis. For example:
Hypothesis: Outlawing alchohol will reduce alcohol related crime, accidents, etc.
Experiment: Through the 18th Amendment, the right to drink is removed.
Data: Crime goes up due to smuggling.
Result: Hypothesis discarded, 21st amendment gives back the right to drink.
Like all theories though, theories on rights require some assumptions...
People from other cultures might not understand this concept.
This is an important point. Though my knowledge of eastern philosophy is admittedly a little thin, individual rights aren't a concept that is as developed there as it is here. I believe that is a large part of the reason why democracy has yet to take hold in eastern countries. From what I understand, some of the leaders of China were confused by the negative reaction we in the West had to the Tienamnen Square massacre because in their culture, the good of the country is what is important.