Not that this is definitive, but maybe some food for thought. How many races do we have, and where did they come from/go?
- Humans and elves - We have Aragorn's line somewhere in this world, and its origin is well-documented.
- Humans and hobbits - Surely we can find some among us that fit the description, and as hobbits are kin to humans, don't see this as too improbable.
- Humans and dwarves - The Variags seem to me to fit the description of such a cross.
- Humans and orcs - Though Peter Jackson sprouted his Uruks from mud, the Uruk-hai and Southerners could be Saruman's cross between orcs and humans, and so this seems to be likely.
So with this, we could see that the races could be still amongst our DNA.
Also:
- Dwarves and hobbits- Could the petty dwarves be from such a mixture?