Progs have no problem with the reality of individual differences but have a big trouble with the concept of group differences. They admit some individuals are smarter than others, but they are reluctant to believe a group can be smarter than another group.
So, if someone says Mike Tyson and Justin Bieber are different in many respects as individuals, even Progs would agree. Tyson and Bieber are different individuals and different as individuals.
Now, suppose some mad scientist clones Mike Tyson and makes a thousand copies of him. Suppose this scientist also clones Justin Bieber into a thousand copies..
Didn't we go from validity of individual differences to validity of group differences?
Surely, the clone-tribe of Tysons are different as a group from the clone-tribe of Biebers.
Of course, people of a race are not clones of one another. There are too many genetic variations. Still, they are kind of like rough-clones of an 'extended family' because they share the DNA that evolved in isolation to make them distinct from other groups.
So, if we grab a bunch of average whites and a bunch of average blacks, whites will have more in common with one another than with blacks, and blacks will have more in common with one another than with whites. Even though there may be more genetic differences between a white giant and a whited dwarf than between an average white man and an average black man, most people don't have extreme-traits --- like Down's Syndrome or some rare genetic condition --- and belong to the racial mean. Among people of this mean, they have more in common with members of their own race(or subspecies) than with members of another race.
Anyway, the Tyson-Bieber Experiment proves that group differences can exist. Just multiply the traits of an individual to form a larger group. Such a group will surely differ from another group with different DNA basis.