Numerous human population genetic studies have come to the identical conclusion, that genetic differentiation is greatest when defined on a continental basis:
The results are the same irrespective of the type of genetic markers employed, be they classical systems [5], restriction fragment length polymorphisms (RFLPs) [6], microsatellites [7,8,9,10,11], or single nucleotide polymorphisms (SNPs) [12]. For example, studying 14 indigenous populations from 5 continents with 30 microsatellite loci, Bowcock et al. [7] observed that the 14 populations clustered into the five continental groups, as depicted in Figure 1.
The African branch included three sub-Saharan populations, CAR pygmies, Zaire pygmies, and the Lisongo; the Caucasian branch included Northern Europeans and Northern Italians; the Pacific Islander branch included Melanesians, New Guineans and Australians; the East Asian branch included Chinese, Japanese and Cambodians; and the Native American branch included Mayans from Mexico and the Surui and Karitiana from the Amazon basin. The identical diagram has since been derived by others, using a similar or greater number of microsatellite markers and individuals [8,9]. More recently, a survey of 3,899 SNPs in 313 genes based on US populations (Caucasians, African-Americans, Asians and Hispanics) once again provided distinct and non-overlapping clustering of the Caucasian, African-American and Asian samples [12]: “The results confirmed the integrity of the self-described ancestry of these individuals”. Hispanics, who represent a recently admixed group between Native American, Caucasian and African, did not form a distinct subgroup, but clustered variously with the other groups. A previous cluster analysis based on a much smaller number of SNPs led to a similar conclusion: “A tree relating 144 individuals from 12 human groups of Africa, Asia, Europe and Oceania, inferred from an average of 75 DNA polymorphisms/individual, is remarkable in that most individuals cluster with other members of their regional group” [13]. Effectively, these population genetic studies have recapitulated the classical definition of races based on continental ancestry – namely African, Caucasian (Europe and Middle East), Asian, Pacific Islander (for example, Australian, New Guinean and Melanesian), and Native American.
Can’t argue with this, but people do.
Counter-arguments come in two forms:
(1) From 50,000 feet, everyone looks the same.
(2) When we drill down to small details and try to find a sharp dividing line, it is all so messy and overlapping that we need to throw up our hands and announce that everyone is the same.
Could you poke a pin in a globe at the epicenters of various “races” and find a pretty good racial match of the world’s peoples with linear interpolations from the epicenters? Jumps (AKA noticeable distinctions between “races”) would naturally happen over oceans or mountains or poles or deserts or whatnot … where there are no people.
Shocking thing is that there are still people not aware about this result and trying to argue that race divisions are arbitrary.
Actually I should say “completely arbitrary” instead of just “arbitrary”. There is some level of subjectiveness involved and the results are not clearcut, just as it’s hard to point out where exactly a sea ends and land begins, or where exactly lays the border between baltic sea and the ocean.