They do.
The doctrine says that the evolution of new species is an infinite natural process with no fixed goal.
The goal is to survive and reproduce.
The choices are that, or extinction.
But even is there are thousands of human variations, all of us are humans and nothing else ... not even apes as some of they say.
All species always remain within their lineage.
Sub-species of humans will still be humans.
Just like humans remain primates, mammals, vertebrates, eukaryotes,....
We are primates because our ancestors were primates.
We are mammals because our ancestors were mammals.
We are chordates because our ancestors were chordates.
Our descendents will also be primates, mammals, chordates.