The North Korean kept evolving from the Prime Koreons traitline, but they who deviated and devolved from the Primes traitline became what we now call South Koreans, aka aberrations.
The differencies between North Koreans and South Koreans are similar to normal people and the africans.
Just like normal people evolved from Homo Habilis, the Africans never did and are still in primtive state and aberrations to mankind, even devolving further and further into chimp-state for every decade that passes.