We are never told specifically, however there’s minor proof that points to the possibility of Karkat’s Group (Beta Trolls) being hatched first as the Originals, with Kankri’s Group (Alpha Trolls) being the re-combination.
First of all, in this scene we have the Beta Trolls being made first- Implying that the Alphas were the subsequent re-combination, and as such, their spawn. Furthermore, however, there’s this panel.
You wish you never pushed those buttons and hatched your team out of all this goddamn slime. You are no ectobiologist. If only there was some other title more befitting of the true discipline you practice, and the death sentence given to whatever you do the disservice of creating. You can’t think of one though.
And what about the OTHER twelve wigglers you spawned? Who were they? Probably further proof this was all meaningless and random. Could it be that they were the true heroes meant to be sent back to play this game, while your team was the superfluous crop? Could a mistake have been made during the reckoning?
This seems to further confirm the order was, indeed, first the Betas (As Clones of Themselves), and then the Alphas (As made from a recombination of their genes). Curiously enough, Karkat IS sort of right in this instance- There was something that happened during the Reckoning, and that is that the energies of the Scratch ensured they were the Heroes rather than have the Alphas become Players at all, erasing their Timeline. They’re not the rejects. They’re the hope the Alphas gave everything up for.
Isn’t Karkat an Alpha? The first of the two universes is the Beta side, with the recombinant players.
The weird part is…the second universe doesn’t even get to “happen” unless the first one fails, which means in a successful Beta session, you’d also have to do the ectobiology. Having it happen in the Alpha session, like with Karkat, REQUIRES the Beta session to fail, otherwise none of them would exist in the first place. But John was a Beta kid who did ectobiology, and they still had to scratch their session.
The Dancestors’ Session is special because it’s Glitched, the fact they needed to do the Scratch to even is a Glitch designed as a calling card to get LE into the Universe, but not much else is explained about this.
As for the Alpha-Beta thing, it’s kind of ambiguous? Calliope refers to their incredibly convoluted Session Chain as ‘From Alpha to Beta, and Beta to Alpha’, Vriska mentions Aranea as her ‘Alpha Sister’, and there’s a few other mentions of Dancestors as the ‘Alphas’. However this may be a reference to them being the ones that went ‘first’ technically, and thus ‘Alpha’ as ‘Original’, rather than Alpha as Alpha and Beta. You could make a similar case to the Dancestors being Beta and Karkat’s Group the Alphas, so I kind of stick with the idea of Karkat’s Group being Betas and Meenah’s the Alphas, to avoid switching around or leaving it ambiguous and confusing.