The differences in IQ between races in America are maintained even among adopted children. And no, I don't think it's because white parents who adopt a black baby are secretly racist and treat their black child poorly.

The problem is that modern black Americans who are the descendants of slaves underwent several selection processes that do not favor IQ. First, they're mostly from central Africa, which is warm. You don't have to plan for the winter, so long term planning is never selected for. Second, they were captured and enslaved by other tribes in Africa, so they're the worst of that bunch, either in terms of social capital or organization or combat technology. Third, they had a harsh voyage and physically demanding existence as slaves, which selects for heartiness over intelligence. Fourth, there was possibly a selection process in the breeding of slaves, selecting only the strongest and dumbest - I'm not sure if this is true and it's not an allowed question in polite society since the answer is either "yes, blacks are genetically damaged", or "no, slave owners weren't that cruel".

Another problem is that melanin directly causes aggression. As in, if you take an animal and inject it with melanin, it will become more aggressive. This is obvious if you look at the coloring of all domesticated animals, which are only bred for docility. Even among breeds of dog - there are no golden rottweilers.

The differences are genetic. To get equality with meritocracy, you would need to roll out large scale a gene therapy program, and one of the side effects of that would be that everyone would end up with lighter skin.