Also, from a scientific perspective, this is a disastrously imperfect experiment. You cannot rule out the effect of the genes unless you control for that. Looking at a group of people who are physically different AND culturally different , then arbitrarily concluding that any differences are the result of cultures is about as unscientific as it gets.
As to the second point, humans are not very genetically diverse. Of course there are enough differences that we can sometimes conclude that a particular person's genes come from an ethnic group, but it's not as nearly as varied as even other primates. Basically, we hit a genetic bottleneck sometime in the past 100,000 years. So it's far more likely to be a result of culture than genes.