100,000 years from now, scientists might discover the bones of today’s Dutch and today’s African pygmies and say:
There’s a height difference of 4.3 standard deviations. This is much greater than the height difference between Homo Sapiens and Neanderthals; the Dutch and the Pygmies must be two different species!
But then another scientist will come along and say:
Height is only one trait. Look how similar their skulls are. Both have nice round skulls compared to the football shaped Neanderthal skulls. Look how flat their faces are compared to the prognathous Neanderthals. So while the height difference might be 4.3 SD, the differences in facial angle and cranial sphericity is so little, so on average, the phenotypic gap between them is much smaller than the gap between either of them and Neanderthals. So these are different races within Homo Sapeins, not different species.
I find it fascinating that despite all the enormous physical variation among different human ethnic groups, we all have the shared phenotype of round cranium, flat face tucked under the brain case, small jaw, and light bones that separate us from Neanderthals.
One of these in not like the other five: