Carlson had stumbled upon Stormfront months ago. As Donald Trump’s election went from unlikely hypothetical to reality, he began tweeting out the disturbing discussions he found—as a call to action for fellow geneticists. “In light of the current political climate,” he says, “I think there’s a much more present danger for our scientific work to become weaponized to enact these ethno-nationalist policies.”

Of course, that is hardly a novel danger. In the early 20th century, Americans used eugenics to justify restrictions on immigrants from southern and eastern Europe. Then the world changed. The Nazis lost World War II and the racial policies they promulgated became abhorrent. Eugenics turned into a cautionary tale.

Modern geneticists now take pains to distance their work from the racist assumptions of eugenics. Yet since the dawn of the genomic revolution, sociologists and historians have warned that even seemingly benign genetics research can reinforce a belief that different races are essentially different—an argument made most famously by Troy Duster in his book Backdoor to Eugenics. If a genetic test can identify you as 78 percent Norwegian, 12 percent Scottish, and 10 percent Italian, then it’s easy to assume there is such thing as white DNA. If scientists find that a new drug works works better in African Americans because of a certain mutation common among them, then it’s easy to believe that races are genetically meaningful categories.

The problem is not with the science per se, but with the set of underlying assumptions about race that we always imprint on the latest science. True, genetics has led to real breakthroughs in medicine, but it is also the latest in a centuries-long effort to understand biological differences. “In a sense, genetics is a modern version of what early scientists were doing in terms of their studies of skulls or blood type,” says Ann Morning, a sociologist at New York University. “We have a long history of turning to whatever we think is the most authoritative sense of knowledge and expecting to find race proved or demonstrated there.” And like its predecessors, genetics is vulnerable to misuse by those with racist agendas.

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In the genomic age, it is now easy to compare the DNA of people from around the world. And it has indeed revealed that our racial categories are fuzzy proxies for genetic difference—an African man may be more closely related to an Asian than to another African. And to put it in perspective, all of the genetic diversity in humans comprises just 0.1 percent of the human genome.

This has inspired the line that race isn’t real—it’s a pure social construction and biologically meaningless. “Yet the lay person will ridicule that position as nonsense,” write geneticists Sarah Tishkoff and Kenneth Kidd in the journal Nature Genetics, “because people from different parts of the world look different, whereas people from the same part of the world tend to look similar.”