What was the Law of God Before Moses and How was It Disseminated?

In Gen. 26:5: > Because Abraham obeyed my voice, and kept my precepts and commandments, and observed my ceremonies and laws. (Douay Rheims) Abraham knew of the obligation to tithe. Noah knew what "clean animals" meant. Abel seemed to know about sacrificing animals (and firstlings). Joseph seemed to know that adultery was a grievous sin. and so forth... What were these precepts, commandments, ceremonies, and laws alluded to in Gen 26:5?? Were they written down? Are they represented in the *natural law*?