Sure, I'll be glad to explain but it might be one of those things that you can really only get the gist of from me; there are books I can recommend though.
Basically, primitive humans found that reciprocating favors and punishing cheaters allowed them to accomplish much more work in a much shorter amount of time than if they all worked as solitary individuals. They could build structures and retain language when they could count on others to pay back their favors in a satisfactory way. That is "fairness" according to nature. Now we even have physical objects to represent owed favors; money. It was a long time getting here but this is where we are now and we tend to forget how cooperation came about but the very notion of "you do this for me if I do this for you" was what got humans started on sharing names, tools, knowledge about plants and animals, as well as techniques for creating tools and eventually machines and medicines.
If there is another notion of "fairness" that is popular among people now, then it is a notion mutated from a very sound origin.