Yet when I look over the replies by liberallarry and P_A_I , I find that they have more than adequately explained this in substantial detail. Both appear quite bewildered as to what more you could possibly want. The lack of clarity on your part further confounds any assessment as to what it is you are looking for.
It seems by your replies to them and to me, that you are in search of something more simplistic or basic than they are willing to waste time trying to explain. If simple is what you want, then lets look at that way.
It should be quite simple for you to visualize a primitive family living by a stream at some time in their past trying to catch fish using only their hands. After a period of time, a better method of using a large rock or log to hit the fish first comes into practice. Still later, use of a spear brings even greater efficiency. At this point we can see a clear development of the concept of right and wrong in getting fish from the stream.
Then after a bountiful harvest of fish, a hill top family comes down to the stream to steal fish. After a victorious battle over the fishing family, they return to their hill top to feast upon their stolen fish and to lick their battle wounds. But wounds fester, and death soon overtakes a few of the victorious family members.
How many times a hill top family will go on to wage such a war with an abundant supply of grapes and berries, is not known. But judging from our history of human capacity for looking out for ones own self interest, it is reasonable to expect that at some point, the idea of trading grapes and berries for fish will come to mind, leading two families to form a tribe to look out for their own self interests.
At this point both families have developed a concept of right and wrong with regard to acquiring the produce of the other. The concept of theft is understood and a low form of morality is clearly in place creating a custom among two inbred families of conscienceless sociopathic people forming a tribe. Since we have no written records from such a distant past, and have never observed the birth of any of the many different kinds of primitive tribes that have been scientifically studied, knowledge here is limited to the theoretical and not the actual. Thus the assumption here that the families are sociopathic and lacking in any kind of individual conscience is not supported. Add individual peoples conscience to the model and morality only would have developed sooner and quicker.
Since you have not been clear as to exactly what it is that you are looking for in an answer, I hope this rather simplistic explanation does it for you. The rest of your questions on this thread can quite easily be figured out by extending this little story to greater complexities of problems. As far as conscience goes, it is possible that it is only an illusion derived out of a trained highly complex sense of self interest imprinted over time from experience, and/or a product of the genetic code built in to our biology by DNA. I tend to think both.
In one sense, I am looking for something "basic", but not in the sense you evidently have in mind. I'm not looking for "simplistic". But laboring under this misapprehension, you decided to "waste time" to explain something I've never inquired into, and when explanations have been repeatedly offered anyway I've tried to get back on topic. In your case, it was a little just-so story about cavemen deciding to make love, not war, and becoming Stone Age James Madisons knowing the advantages of union. I doubt very much it ever happened like that, but that's beside the point. Somehow or another, people behave "morally". Great. Never argued otherwise. But why, for you, does morality even make sense as a concept? Why does the later behavior have a different status from the earlier?