Races

[Cleretic]

Someone else here will surely be able to name the exact source (or correct me if I'm wrong), but I believe supplemental material describes the sundered races of men having developed their unique characteristics based on their ecological circumstances (I understand that's basically just a broad description of the concept of evolution in general, but it's what we've got). Coincidentally, though, they all happened to evolve into identical races even on the other shards (at least the ones we've seen, and it looks like you've completed ShB, so you've seen the First). Which does make that explanation a little harder to swallow, but... this is fiction, and making unique races for each shard we visit is more resource-intensive than the devs are interested in investing in, clearly lol.

Never say never, but I suspect we're unlikely to be given anything more in-depth than that. Plenty of room for speculation, at any rate!

Live letter Q&A! I think it makes sense that every race developed concurrently across every shard, because every shard had essentially the same basic conditions; it makes sense that elezen developed on all of them, because the conditions that would've led to those traits dominating would've been present on all shards. It's carcinization, but with bunny people. It's a fantastical version of it, but it makes enough sense to buy.

You've also got the more specific situations of the sub-races, where cultural or geographic differences led to a split, which might be to the OP's liking. Wildwood and Duskwight elezen stem from an ideological split that happened around Gridania's founding, Rava and Veena viera live in different places and are implied to have different social dynamics regarding outsiders as a result. Hellion and Lost hrothgar are my favorites these days, where it's not really a 'split' so much as an intra-community social dynamic that outsiders misinterpreted; the Lost are just hrothgar whose queen has died and they don't currently have a new one, they aren't really treated differently or have a different dynamic, demographic or genetic makeup to other hrothgar. But because a fairly large hrothgar family with white fur recently had their queen die, there's just a statistically anomalous amount of white-furred Lost right now that led outsiders to assume Lost have white fur as a rule.