I was motivated to ask based on the answer to another SE Biology Question that uses the following argument to conclude that two varients of snake are indeed a different species:
To test whether [Dendrelaphis ashoki and D. girii were a separate species of snake] they (Vogel and van Rooijen, 2011) compared 9 individuals of D. ashoki with 34 individuals of D. pictus, and found statistically significant (p<0.05) differences in five morphological characters....
The authors didn't rely just on morphological evidence: they note that D. ashoki, which is found in the Western Ghats, is also geographically isolated from other populations of D. pictus, which are found in Northeast India, Myanmar and South East Asia.
My question is, why can't we on the bases of an analogous argument conclude that (say) Eskimos & Kalahari Bushmen are, forget the race debate, but two entirely distinct species?
I mean if "number of infralabials touched by the first sublabial" can count as a legitimate species-distinguishing morpohological factor, then so can heights, eye colors, hair texture, skin color etc. right? And we won't even have to fish too hard to gain statistical significance given how different Eskimos are from Kalahari Bushmen morphologically.
Further, the geographical isolation must have been pretty strong too.