The Hist are literally the only spacefaring species now that the Dwemer are Gone. That's how they got to Tamriel in the first place.
Hell, if you want Spelljammer Scrolls that's your way of making it happen lore-wise.
The way I remember it, the Dwemer never went to space, unless you call any plane walking spacefaring, but then just about every accomplished mage ever is an astronaut.
If we're talking actual space
fareing, though, there's both the Imperial Mananauts and the Sunbirds of Alinor, men and altmer respectively. The Empire even had a functional space station where they trained their battlemages, that's where the Battlespire game takes place.
I recall some old book in either oblivion or skyrim that hinted at the possibility of khajiit and argonians being able to produce offspring with humans/elves. If that is indeed possible, then that could explain where the lizard boobs come from, if a portion of the population has, even if they didn't realize where they got it, human genes.
Generally, in the TES-verse, hybrid children take on the race of the mother. "Hybrid races" such as the Breton coke into being either through a metaphysical intermingling of ideas and myth rather than something carnal. Or, if you prefer it that way, over a really, really long time of having mixed offspring.
Don't hate on Altmer, they aren't all nazis ):<
I guess they could be secret Thalmor - haha I'm kidding, individual Thalmor have no subtlety. They must twirl their moustaches. While the greater organization is surprisingly insidious...
In a way, it's genius. They act like openly malicious powerthirsty oppressors on the surface, and make everyone think that's the be-all-end-all of the Thalmor ideology, when in reality their ultimate secret plan is to destroy the universe. Like, holy shit.
Don't believe that human propaganda. They don't want to destroy the the universe, they want to
save the universe and restore everybody to greatness
by destroying the universe#MakeAltmericaGodsAgain