Consider the success of race-based medicine. To take a very simple case, black people are more likely to get sickle-cell disease (鐮形細胞貧血症). The reason is that carrying the gene that can lead to sickle-cell disease also makes one less (more???) likely to catch malaria, such that people whose ancestors evolved in areas where malaria is relatively common are more likely to carry the gene that can lead to sickle-cell disease. Black people are more likely to have ancestors who evolved in such areas, because malaria is most common in sub-Saharan Africa. Here is a relevant genetic difference, not one relating merely to morphology. This seems a good reason to reject the second premise from the argument from genetics.