ABSTRACT
The genetic work that was expected to provide the validation for dividing humans into races instead undermined it. Genetic variation is to the largest extent polymorphism, and not polytypism. The fundamental units of the human species are populations, not races. Nevertheless, populations differ from one another in the frequencies of the same alleles they carry, and this can be used to group human populations by genetic similarity. Like morphological differences across the human species, these groupings are generally obvious when extremes are contrasted, but otherwise there is little in the way of reliable biological history to be inferred by genetics.
