Might be worth noting that if you look at a place where a person's income is a function of their productivity (i.e., smart, hard working people make more money

Might be worth noting that if you look at a place where a person's income is a function of their productivity (i.e., smart, hard working people make more money on average) then you should expect some stickiness, because one's intelligence and work ethic surely is correlated with the same qualities in their parents (and that's regardless of whether you believe in genes or nurture).