To add some nuance to the “black person fast” rhetoric here…

There is a higher degree of genetic variation among humans in Africa than across the entire rest of the world. This is because humans first evolved in Africa, some 300 000 years ago, and then first left Africa some 60 000 years ago. So Homo sapiens spent about 80% of their existence in Africa alone. (Though other hominids left Africa earlier and did later interbreed with Homo sapiens such as Homo neanderthalis and Homo denisova.)

So this means that, crudely, if we were to plot the “inherent genetics-based” speed of humans from different continents, Africans would likely have the flattest, widest bell curve.

Then because the Olympics approximately selects for the most elite athletes from each country, you can imagine that like taking the right-most fraction of each bell curve from each continent. Then of those subsamples, we’d expect that the Africans would be fastest, though population size would also have an impact. Same for things like tallest and shortest and other traits closely linked to genetics.