Arguments over monogenesis and polygenesis developed as early as the 15th century. Enslavers, motivated by the economic desire to colonize and reap economic benefits from land overseas, sought racist justification for enslavement. King Afonso V of Portugal commissioned Gomes Eanes de Zurara to write what Kendi calls “the inaugural defense of African slave-trading” as Eastern European Slavic peoples, who Western Europeans traditionally enslaved, defended their land with more success (23). In the wake of Zurara’s book, Kendi writes that “Western Europeans began to see the natural Slav(e) not as White, but Black” (23).

Many of these defenses took on theological, or missionary, importance. But scientists and political scientists, from Locke to Sir Isaac Newton, began to seek scientific explanations for the unequal humanity they saw in the world around them. Monogenesis, the idea that all humans share a common origin, competed with polygenesis, which contended that white and black humans were of different species. With the rise of Darwinian biology, Social Darwinism and eugenics revitalized arguments of polygenesis in the popular imagination. Religious Southern slaveholders, generally fixated on retaining power more than faithful coherence, toggled between standpoints.

Kendi traces the monogenesis and polygenesis debate, and the scientific study of race, to the present day.