I would hope the US was able to retify the wage gap in the next 1000 years, so you wouldn't get your selective patterning. However, most people take too simiplistic/straightforward view of evolution. We aren't one uniform blob of code, as individuals, our cells vary in both expression and content. We can receive genetic infusions sideways via virus and bacteria. Recessive/malform gene expressions add heartiness to the species and allows for a stronger genetic match in the future. For example, in einkorn wheat, 'a winter wheat', the genes for cold resistance were introduced via a plant that had substandard yield.
I would set the rise in modern medicine back futher than antibotics (1908) to the discovery of bacteria in 1676. That started modern hygene and world life expectancy has skyrocketed since then from 25-30 to 67. There are 15 countries with a life expenctancy over 80 and 127 countries over 67, 151 over 60, and 18 under 50. Africa drags the average down still due to lack of basically everything we take for granted (peace, utilities, etc).
The US has a life expentency for whites/blacks/all Americans has been 72/64/71 in 1970, 74/68/74 in 1980, 76/69/75 in 1990, 77/71/77 in 2000, and 79/74/78 in 2010. Without exogamy, the prevalence of sickle-cell anemina and STDs in the African American community won't allow their 'better parts' to survive and 'breed quality'. Over 1000 years, if present conditions remained (under replacement birth rate, higher minority morality rates, high Latin and Asian migration), you might see the demographic group disappear entirely.
If you want to be racist, you are better off doing it by haplogroups than skin tones or nationality. For example, Watertowers ascertation that Sweden can be socialist because of their good genes, makes me wonder why Bosnia and Herzegovina, which also have a predominance of Haplogroup I (
http://en.wikipedia.org/...on_Haplogroup_I_Y-DNA.svg), does not also have the same luxuries. It may have more to do with the fact of not infighting extensively allows a nation to find stability and prosperity.