Go take a look at the various declarations of secession when the slaveholding US states tried to quit and form the Confederacy. A number of them explicitly mention that a system of racial slavery is fine because black people were naturally inferior, which is how in the 1850s one would have said "biological differences". That was very obviously politics.
Further, there's an enormous history of explaining why people on the short end of a power differential truly deserve it because of their inferiority. You could look at all the talk around the time a century ago when men were deciding whether women should be allowed to vote. Women's "biological differences" were a huge reason they supposedly couldn't handle political power.
For those interested in the history, Kendi's "Stamped from the Beginning" is an excellent history of how ideas about "biological differences" have, since the ancient Greeks at least, been used politically. The particular "biological differences" change, of course. E.g., the Slavs, from whom we get the word slave, were considered naturally inferior by the Greeks because they came from a colder place. When enslaving Africans became an industry for people from the north, suddenly the problem was Africa's hotter climate. The "science" keeps changing, but what doesn't is the result: "inferior" people deserve less social or economic power.