Could it be possible US-Asians study more, because they are more intelligent or are raised by more intelligent people? My point being, it is very likely both genetics and environment, and it's not rocket science to assume smarter parents are going to create a more intelligent learning environment and/or attitude in their children.
Here:
http://datacenter.kidscount.org/dat...73,869,36,868,867/10,11,9,12,1,185,13/432,431
That's a link to a charity ( I think) displaying single parenthood rates in the USA.
Asians, who tend to perform the best academically, have the lowest (surprise surprise) single parenthood rate in the USA, sitting at 17%.
Here is an article, regarding what happened to an elephant population in Africa in the absence of adult males in the herd/area. There are a lot more on this subject, but I can't be bothered to find right now. PM me if you want me to as they are pretty interesting.
http://thesestonewalls.com/gordon-macrae/in-the-absence-of-fathers-a-story-of-elephants-and-men/
Basically, in the absence of adult males, younger males acted more aggressively and actually had a physical increase in testosterone. When an adult male elephant was put back in to the area, all of the young male elephants testosterone dropped & they coincidentally started behaving themselves again.
When you look at this, then look at the single parenthood rate in american populations, it isn't surprising that the single parenthood figures also correlate with crime rates within the relevant populations.