mamba
Legend
That says nothing about the human part being anything else than what we are familiar with.I don't really understand your objection. You asked where the rules say that D&D humans are not humans as we know them. I showed you where the rules clearly state that D&D humans often show traits of other species, such as elves and orcs. Humans as we know them cannot have such traits. Therefore, these are not humans as we know them.
We do not know those mixes per se, but when you see what a Half-Elf or Half-Orc is like compared to a human, and then water the difference down considerably because we are talking four generations back with everyone else in the family tree being human, then the result is back to being indistinguishable from a human.