Re: Why no comment on the number of human species?
A species indistinguishable from humans externally may be a different species. One indistinguishable by a tricorder is not. One wonders how many of those "not from Earth" humans were actually bona fide members of H.sapiens who had just ended up off-Earth for one reason or another.
In any case, we don't know if humans originated on Earth. Supposedly Earth even in Star Trek has the appropriate fossil track record - but it need not establish the birth of H.sapiens here. Might be just a case of a humanoid species or three emerging here, and then being replaced by an imported sapient species that isn't really related to the three it replaces (but the galaxy-spanning genetic commonality of "The Chase" fame throws the researchers off).
Or then there's no fossil record to speak of, and Trek paleontologists are just guessing. We do know they are saying that humans come from Earth even in the 24th century, as per VOY "Distant Origin", but that doesn't automatically make them right.
"All Good Things" pretty much puts that to rest since the whole point of the episode was that the anti-time anomaly was large enough in the past to prevent the basic molecules of life from ever bonding on primeval earth. Thus preventing the rise of the human race.
Well maybe I'm the faggot America.
I'm not a part of a redneck agenda.
Now everybody do the propaganda.
And sing along in the age of paranoia