Addiction among American Indians

I ran across a new study reviewing the research on race and addiction. The authors find that: 

In these studies, both past year and lifetime rates of alcohol, nicotine, and drug use disorders were consistently higher in Native Americans and lower in Asians,with Blacks, Hispanics, and Whites in between. 

It looks like any theory of American Indians (AIs) that limits itself to alcohol (e.g., the notion that AIs have not been exposed to it long enough to adapt to it) is missing part of the story. Addiction to drugs in general tends to be more common in this population.

Also--the stark differences between Northest Asians and Natives--addiction differences being only one illustrative trait--show how quickly significant genetic change can occur (the differences surely can't be 100% due to environment). It's not like these groups split 100k years ago.