[DF] Elves

[(E)]

Playing on that idea.
Elves can sub-consciously alter the DNA of their progeny. Taken to the next level you have elves that can consciously alter/select (some of) the DNA of the next generation.

[AlexanderHowl]

Or it could be that elves are more vulnerable to the mutating effects of the subtle aspecting of mana by the local environment. While the mutations would take one hundred generations among non-elf races, it would only require one generation among elves. The rapid mutation rate of elves could even explain the sheer number of non-elf races, as each non-elf race would be descended from a group of elves that eventually mutated into a non-elf race without that specific vulnerability.

[ericthered]

In my current game (which is certainly not DF), elves all have the same ancestry, but they physically change themselves depending on where they live using magic. So they all have the same language and the same history, though the culture is pretty different for different groups.