Well it all depends
You know, on earth, sometimes one country has several climates, like how America has both tropical and snowy
It's the same for Tera. It was also caused by natural selection. And also the fact that over on Tera, their DNA actually "knows" what traits to code for to fit an environment, unlike mutations on earth which are ALWAYS random, on Tera, it can be random OR it can be "chosen" by their DNA