That article is pretty much crap. Basically every sentence in it has a problem.

Sure, the author starts with some basics such as mutation rates and isolation of populations but then he proceeds to discount anything that might run against his thesis and over credit anything that he can dig up that might support it. It would take the better part of a day to go into a line by line analysis on the matter.

For starters, he is on about effects that have only existed for the past several decades or for at most a few centuries. The short time horizons are such as to be an eye blink on the scale of time which evolution is operative.

Second, he fully discounts isolation of populations as either non existent where he can or irrelevant where he cannot. OK, what about the child of an automotive mechanic in New Jersey? Is that guy going to marry an East African princess?

Generally no, that is going to be fairly rare and thus the two populations are not likely to mix to the point of becoming part of the global average. Although I will state that I picked that specific example because I happen to know the lucky bastard who did exactly that. His kids will enjoy a genetic diversity unlike the guys he went to high school with. Cultural values considered, he is also probably going to end up having kids with dozens of women in Africa. So he also gets a good healthy dose of spreading his genes in the way that the author says has ended.