Humans as the Oldest Ancestry

Most fantasy fiction -- from folklore to Tolkien to D&D -- frames elves and dwarves as the older peoples, and humans as (relatively) recent arrivals. The very first sentence of the “human” description in the 2014 5E player's handbook says as much, calling them “the youngest of the common races.” But what if the opposite is true?

Suppose that the other humanoid ancestries are derived from the common baseline of humanity. This explains the many creatures who are very clearly “human crossed with something else.” Obvious examples are merfolk (human and fish), lizardfolk (human and lizard), and aarakocra (human and bird). Long ago humans were changed by some kind of magic, and those changes persisted through generations. 

Consider the 2014 5E Monster Manual's half dragon: a first generation product of such a union. After many generations, the result is dragonborn. And the same is true for the dwarves, elves, and other more common ancestries; perhaps elves originated with fey magic, and dwarves with earthen elemental influences. 

For example, many humanoid creatures can procreate together either as a matter of course, or with the aid of trade magic (facilitating inter-ancestry procreation is a common services trade magicians supply). Take this to its logical conclusion, and dwarvish traits only persist as long as dwarves continue to have children with other dwarves, generation after generation. If a group of dwarves moves to a human city and intermarries with humans, their offspring will be more and more human-like by the generation. This is already implicit in the game’s treatment of half-elves and half-orcs, taxonomic categories that I strongly dislike. “Humans as the Oldest Ancestry” fixes those problems.

Yes, this kind of thinking can be taken too far. Genealogy and trait inheritance is going to be vague in a world where “a wizard did it” can answer such a broad range of questions. But a little goes a long way in creating a more interesting world.