GURPS Humanity lists the Acheron, Answerin, Azhanti, Darrians, Dynchia, Floriani, Geonee, Iltharans, Irhadre, Kargols, Luriani, Nexxies, Qtrai, Syleans, and Yileans. All of these are marked as 'Canon' in the Wiki.
Acheron are a Variant Human Race, not a Minor Human Race (they were created by the Solomani, not the Ancients). It appears the Solomani aren't as good at the whole process, since the Acheron aren't a happy lot, on the whole.
Answerin could be anything really. Note that they share some blood types with the Vilani, which I suppose makes sense, as they're in Vland Sector (there's some overlap with Thaggeshi too, who are also in Vland. Presumably the local Ancients were working with similar base stock in all three cases, at least to some degree)
Azhanti are extensively modified to the point that it might be difficult to tell what the original template was. I imagine they selected equatorial populations as a base, though. Note that they have some overlap in blood types to Irhadre -- who are from an arid environment -- and Zhodani (Zhdant is rather arid, no? No idea if this means anything; do these blood types hint at descent from a particular species or subspecies judged suitable for heat and aridity?)
Darrians can interbreed with Homo sapiens, even if the young inherit either promelanin or melanin (you can be a gold half-elf or a brown half-elf; I guess the latter can often pass as standard Imperial Man). Apparently a lot of the Darrian traits are traced to retroviral agents on their world. No idea what the base stock was, but presumably there was a lot of Homo sapiens or something closely related in it.
Dynchia are heavily modified to the degree that their base psychology has been significantly altered (the common denominator appears to be the removal of a territorial-protective impulse). So, much like the Azhanti, I imagine it's difficult to pin their origins down.
Floriani are fake Humans created by the Ancients wholescale from Human DNA. As I like to note, they took Human DNA and used it to create a Human. This is both utterly brilliant and the most unimaginative thing ever, and so is completely suited to the Floriani.
Given the name "Florian", the Solomani obviously have the old Indonesian species in mind, given the Barnai's diminutive size, though whether they're on to something there I couldn't say.
Geonee, could be anything? We know a lot about them, but not their ancestry (maybe because they keep listing "Ancient" on the census). Incidentally, Geonee are one of the gaps on the Human Blood Groups page I've been maintaining on the wiki.
Iltharans are apparently adapted from populations in colder climes than most, and are relatively infertile. (As an aside, Iltharans are one of the Human races crying out for some further exploration, they have quite the interesting history).
Irhadre, no idea, but presumably whichever human species or subspecies was best suited to desert conditions was used as a base. As noted, blood types overlap with Azhanti and Zhodani, which might be relevant? One wonders where the Jonkeereen adaptation treatments came from when the Imperials decided to "perfect" the process of desert humans.
Kargols are explicitly of largely Neanderthal heritage. The question is, can they breed with Suerrat or Ziadd? Volunteers for these experiments please contact the For Traveller Science Institute, we can promise discretion.
Luriani are now a distinct species, Homo luriani, but which stock was used initially I have no idea.
Nexxies and Otrai are also Variants, not Ancient-descended. Otrai have Solomani stock. Nexxies are Imperial Man stock.
Syleans are given to albinism, so that might be a clue?
Yileans are adapted to high UV -- skin is blue-black -- so I imagine they might have originated with a species or subspecies suited for that?
EDIT: The Blood Types page --
https://wiki.travellerrpg.com/Human_Blood_Types. I need to update the references, but it's all taken from other sources, no speculation on my part here.
