It's not evolution.
(I had this argument about marvel comic mutants just the other day.)
In DS9 they were saying that there are genetic differences between Romulans and Vulcans, which can't happen whole sale across the board from just 2000 years since the age of enlightenment if they breed 10 to a hundred times slower then humans...
The Vulcans will
themselves into an emotionless sexless state.
That's not even Eugenics, I'd go so far as to asusme that it's religion or politics.
But it most certainly wasn't a logical reaction to consistent environmental forces.