^gene flow between human populations around the world prevents that from happening. same as any other species.
i should clarify when i say social construct i don't mean it's just made up. but basically it's just a categorization of humans we did before we knew anything about genetics and we did it pretty much on the basis of physical attributes. that doesn't mean the differences aren't real but they are as far reaching as many people tend to think they are.
i saw you saying that negroid etc might be a more useful scientific term but pc won't allow it. maybe it is useful as frownland said for anthropological reasons but there isn't any distinct 'negroid' genetic group. basically our environment shapes a number of our more visible attributes in a more direct way and so there's a good deal of variety in the physical attributes humans have as they have to survive in different environments. but these differences are most apparent in measuring superficial attributes and resistance to certain regional diseases.
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