> I think the underlying mechanism is simply natural selection

Genetic natural selection takes thousands of years, or at an absolute minimum multiple generations. Social selection occurs far more rapidly, often within a single generation. A person born in the 1950s that is genetically predisposed to manual labor may do well for the first few decades of their life, but as society changes and starts valuing white collar work more, they will do far worse. Their genetics didn't change, but society did.

Those that favor nature over nurture vastly under-estimate the time-scales which it takes natural selection to occur as compared to social selection.