Origin: A Genetic History of the Americas

People who live closer to each other are more likely to marry and have
children than people who live far apart from each other. Thus different
alleles—versions of genes—are dispersed gradually following a pattern that
geneticists call isolation by distance. Some traits—and underlying genes—
show the effects of natural selection in particular environments. For
example, in high-altitude environments natural selection operated to
increase the regional frequency of genetic variants that help people
withstand the effects of hypoxia. These patterns are then further
complicated by our species’ prolific histories of migration, which nearly
always results in admixture. Contrary to the typological framework that
underlay the work of early physical anthropologists, ancient DNA shows us
that no population throughout human history has ever been “pure” in a
genetic sense (35).
The combined effects of these evolutionary forces—natural selection,
genetic drift, mutation, and gene flow—overlaid with our history of
migration (or, alternatively, persistence in one area) and cultural practices
have all influenced the patterns of human variation that we see today. By far
the most variation—genetic and phenotypic—is present in populations that
live in Africa, the continent where humans like us originated. Genetic
variation generally decreases gradually in populations with greater
geographic distance from Africa, reflecting our species’ genetic legacies of
migration, with additional adaptations to new environments. The categories
of white, black, Asian (or Caucasoid, Negroid, and Mongoloid) do not
accurately reflect these complexities (36).
But just because race is not a scientifically accurate way to categorize
human variation does not mean that race isn’t “real”—although it is a
construction born of a specific cultural history, it is real to all of us and
shapes our lives in profound ways (37). The horrific treatment of the
Indigenous peoples of the Americas and their ancestors is just one example.
The Origins of Native Americans
Following in Morton’s footsteps, Hrdlička believed that the study of human
skeletons—particularly skulls—could answer the controversial question of
the racial origins of Native Americans. He and his colleagues, including