Variable based on the game. In modern d&d humans are the least specialized, while in old d&d (like 2e) humans were mechanically Inferior until higher levels, where they had the highest level cap. Also demi-humans (elves, dwarves, etc) were fewer in number, Tolkien-style, and sometimes discriminated against. In fact it kinda seemed like the less liked a race was, the more inherent abilities they had.
Wine and Valium were a housewife's best friends back then.