The Golden rule is just the more familiar name for the Ethos of Reciprocity. There are both positive and negative forms found through history in any culture that learned to socialize well.

There is no question that things like the 10 Commandments and The Golden Rule predated not only Christianity, but all organized religions. Social interaction, morals and laws evolved just like everything else. In primitive societies, they just did not have the luxury of adult males fighting and killing each other. Thou shall not covet another cave man's wife's ass had a practical application. Tribes who developed laws of social behavior that kept the adult males from slaughtering each other had an advantage via natural selection over those who did not. Chaos and violence within the tribe was selected out. Others just did not survive. I know this is over-simplification, and is just an example. No gods or religion required.