Human races as human variation
Arguments against the existence of human races (the taxa 'Mongoloid', 'Caucasoid' and 'Negroid' and those from other classifications) include those stated for subspecies10 and several others15. The within- to between-group variation is very high for genetic polymorphisms (85%; refs. 16,17). This means that individuals from one 'race' may be overall more similar to individuals in one of the other 'races' than to other individuals in the same 'race'. This observation is perhaps insufficient18, although it still is convincing because it illustrates the lack of a boundary. Coalescence times19, 20 calculated from various genes suggest that the differentiation of modern humans began in Africa in populations whose morphological traits are unknown; it cannot be assumed from an evolutionary perspective that the traits used to define 'races' emerged simultaneously with this divergence15. There was no demonstrable 'racial' divergence.
Y-chromosome and mitochondrial DNA genealogies are especially interesting because they demonstrate the lack of concordance of lineages with morphology15 and facilitate a phylogenetic analysis. Individuals with the same morphology do not necessarily cluster with each other by lineage, and a given lineage does not include only individuals with the same trait complex (or 'racial type'). Y-chromosome DNA from Africa alone suffices to make this point. Africa contains populations whose members have a range of external phenotypes. This variation has usually been described in terms of 'race' (Caucasoids, Pygmoids, Congoids, Khoisanoids). But the Y-chromosome clade defined by the PN2 transition (PN2/M35, PN2/M2) shatters the boundaries of phenotypically defined races and true breeding populations across a great geographical expanse21. African peoples with a range of skin colors, hair forms and physiognomies have substantial percentages of males whose Y chromosomes form closely related clades with each other, but not with others who are phenotypically similar. The individuals in the morphologically or geographically defined 'races' are not characterized by 'private' distinct lineages restricted to each of them.
