Who are more archaic? Vietnamese or Thai?
Thai, I think. Thais transitioned to Neomongoloid probably only 900 YBP. Vietnamese transitioned to Neomongoloid 2,300 YBP. The more recent the transition, the more archaic features will be preserved. The older the transition, the more the archaic features will tend to have gone out. This is because generally humans sexually select for progressive features and against archaic features, at least nowadays anyway.
Southern Chinese – Most progressive Southern Neomongoloid with few if any archaic features. Transition to Neomongoloid probably 4-5,000 YBP.
Vietnamese – Moderately progressive Southern Neomongoloid with some archaic features. Transition to Neomongoloid 2,300 YBP.
Thai – Least progressive Southern Neomongoloid with more archaic features. Transition to Neomongoloid 900 YBP.
In all three cases, the previous stock that transitioned to Neomongoloid was probably an Australoid type, even in Southern China. This is why Afrocentrists go on and on about “Black Chinese” – there were quite a few dark people with frizzy hair in Southern China 5,000 YBP.
Vietnamese certainly transitioned from a Melanesian type. The earliest Vietnamese skulls from 22,000 YBP are clearly Melanesian.
Thais probably transitioned from some sort of an Australoid type, but it’s not known which. It may have been a Veddoid type.
In the case of the Vietnamese and the Thai, the transition to Neomongoloid occurred as a consequence of a mass invasion or movement of Southern Chinese into their regions.
There was a huge invasion of Vietnam by Cantonese Chinese 2,300 YBP. That is why Vietnamese is full of Cantonese borrowings.
There was a very large movement o unknown character by Yunnanese Chinese into Thailand 900 YBP that appears to have significantly changed the Thai phenotype.
The case of Southern China is less clear, but as Northern Chinese transitioned to Neomongoloid 9,000 YBP, 4,500 years before the Southern Chinese, the Southern Chinese transition to Neomongoloid probably occurred due to a mass movement of Northern Chinese to the south. But that is only conjecture.
Also more progressive phenotypes tend to have higher IQ’s than more archaic phenotypes. I am not exactly sure why that is honestly.