I believe that all humans have the inate ability to now right from wrong...most cultures if they believe in a god or not have a moral code..knowing that it's wrong to kill, it's wrong to steal, so on and so forth...so does one have to believe in god to understand what morality is? No I don't think so... it is in our DNA to know, but it's up to those who are more mature to help the little ones along. Most societies have some understanding of how to teach their young how to assimulate what they feel is right and wrong. But remember we might not understand what the cultural values are when looking from the outside in with our own cultural values that we were raised with.
Canabals that were ask if its wrong to kill and eat people said yes. When asked if it was wrong to sleep with someone elses wife, they replied yes as well. They were never influenced with another cultures values, but yet knew right from wrong. The Waodani knew that it was wrong to kill as well but did it anyway.
This is why I think Gods moral laws were placed in mans heart besides the fact the Bible says so.
I guess you could argue that somehow thats been remembered since back before the tower of Babal.