These individuals reject white supremacy but are also opposed to identity politics and political correctness. Harvard cognitive scientist Steven Pinker, for example, has received plaudits from “alt-right” figures for questioning those who raise issues like gender and racial representation in science.

Centuries before the rise of the alt-right, Thomas Jefferson, author of perhaps the most famous words of the American Revolution — “all men are created equal” — also believed that black people were “much inferior” to white people in reason, comprehension and imagination. This may help explain how Jefferson was able to pen the Declaration of Independence and also own hundreds of slaves over his lifetime.

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That American luminaries like Jefferson, who believed genuinely in individual freedom, used science to justify a legal framework that granted rights and citizenship according to the race doesn’t mean all Enlightenment ideas are racist. But it does show how identity politics and racism went hand-in-hand during a period we’re fond of referring to as the Age of Reason.

Today progressives and “alt-right” rationalists squabble over whether race is a “social construct” or biological fact — a false and misleading dichotomy that arises more from methodological turf wars than from an understanding of how the concept of race has changed over time. But our contemporary notion of race was actually born in the Enlightenment, at the intersection of science and identity politics. The Enlightenment-lead shift in our understanding of race laid the foundation for how we understand racism today.

Faced with the conundrum of believing in individual liberty while living in societies that reaped the fruits of the Atlantic slave trade, Enlightenment thinkers from Voltaire to Johann Blumenbach created a human taxonomy. This system categorized Caucasians as, in Blumenbach’s words, “the most beautiful race of men,” while the African man was labeled, in Voltaire’s words, an “animal” with “a flat and black nose with little or hardly any intelligence.”

Voltaire’s description is particularly telling, as it aligns observable characteristics (phenotype) with an unrelated and unscientific impression of character and diminished intelligence. This is a textbook example of scientific racism, the misapplication of scientific knowledge to justify a belief in white supremacy.

Whereas throughout much of the 18th century the word “race” was used to describe national and geographical identity, not skin color, Enlightenment thinkers like Blumenbach introduced scientific theories that applied taxonomy to human traits, drawing on the influential work of Swedish scientist Carl Linnaeus.

But Blumenbach took Linnaeus’ biological classification system a step further by creating a hierarchy of worth based on physical appearance, forever altering the concept of race.

These theories lent legitimacy to the stereotypes on which slavers relied to hold human beings in bondage and keep the slavery economy running. Phenotype or differences of appearance are not Enlightenment constructs, of course. But it was during the Enlightenment that certain characteristics — like skin color and facial features — became widespread signifiers of character and intelligence.