I'm not sure about any cell mutation business with regards to natural selection. The people with the alcoholic genes in a culture would eventually die off (not entirely, obviously) if given sufficient time. From what I have read, the Italians and Jews have had the longest amount of exposure to alcohol, hence their low alcoholism rates.
Your Chinese/Native AMerican comparison only supports my theory...Chinese have had access to alcohol since before recorded time (as per what you wrote), wheras NA's have only been exposed for 300 years. That supports my theory on why the chinese are low on the scale and the NA are high: time exposed.
I believe I am an alcoholic because it is in my genes. I come from a long line of hardcore drunks. Most either died to young for health reasons, or committed suicide. We just don't survive.