Superficial difference

1) humans are 99.9% genetically the same
2) the small differences in the genome that do exist determine the interface between the individual and the environment, eg. skin colour, body shape, eye folds, disease resistance, etc
3) while the body's APIs may have adjusted to different environmental forces, the underlying processes and systems are the same

Good taste prevents me from drawing an analogy between the ability of different human communities to interbreed and attempts to reconcile the interface incompatibilities of identity systems.