There is a simple explanation for differences in abilities between groups that has nothing to do with their genetics are so-called natural ability: the fact that groups often grow up around other members of their group. Both nature and nurture are largely in common for many groups, so it could easily be either that causes the observed differences in ability.
could easily be either
Or both. They're not mutually exclusive. Do Jamaican sprinters excel because they grow up around other sprinters or because they are blessed with natural ability? Yes. Simply put, or != xor.
That's a pretty view, but it's inconsistent with reality, and radical egalitarians need to come up with increasingly implausible explanations to explain everyday circumstances that make perfect sense once you drop the blank slate model.