Humanity today forms a single species and can interbreed freely. Differences in color of hair, skin and eyes are largely due to differences in the qu… - Isaac Asimov

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Humanity today forms a single species and can interbreed freely. Differences in color of hair, skin and eyes are largely due to differences in the quantity of a pigment called melanin, and this does not affect humanity's essentially unitary character. Nor do differences in the shape of the eye or nose, in the shape of the skull, or in height.