We'll start with the obvious.
Skin doesn't just keep your organs in and have different shades. It also basically photosynthesises vitamin D. So, in more northerly climates, with shorter days and such, black people are vastly more likely to develop rickets.
Muscles are the next. There are observed differences, though the observation of these alone have been declared racist. But, the differences in muscle and bone is the main reason most successful olympic runners are black and most successful olympic swimmers are white.
Blood has similar divergences, in that sickle cell anemia is vastly more common in blacks. Heart disease from obesity sets in faster.
A lot of the problem in pinning it down though, is that science as a whole is dominated by leftist thought, and leftist thought DEMANDs that race be a social construct.
And in a way, they're right. Race is a nebulous and inefficient term. More accurate would be discrete breeding population.
You see, they maintain that 200,000 years in relative isolation produced no changes to the organism, because special pleading.
Obviously, full speciation did not occur, but there are also examples of fertile hybrids of distinct species in nature. Not everything results in a mule.