Editing Half-Elf (section)

===Implications for how humans, elves, dwarves, etc. are related===
In real life, two species can only make a hybrid if they are still in the same Genus, the taxonomic level just above Species. This is why horses can have babies with donkeys, but not with dogs. In fact this is how we ''determine'' whether two species are in the same genus or not: if they can have ''grand''kids together, they're the same species, at most different subspecies; if they can have kids, but those kids are themselves infertile (more on that later), they're the same genus, but different species; if they can't have kids period, they're in different Genre and we'll have to do other, more time-consuming procedures to figure out how they're related (which is what we have to do from the get-go in the case of organisms that don't reproduce sexually, such as bacteria).

In most fantasy settings this isn't a problem, since elves, dwarves, halflings, gnomes, etc. usually look exactly as different as you'd expect another species in the ''Homo'' genus to look, however it also means that if humans and elves can have kids, then all other possible combinations should produce a kid as well.

That said, there's a little-known phenomenon that could be used as a partial workaround: Ring Species. A ring species is one that's ''in the process'' of diverging into multiple distinct species but isn't quite there yet, such that individuals of population A can have grandkids with those from B, B can have grandkids with C, but A cannot have grandkids with C. So it could work if dwarves were A, humans B, and elves C, but only for a setting where elves and dwarves are completely isolated from one another somehow; this arrangement would never arise in a setting where elves, humans, and dwarves are frequently found together in the same city.