[‘Could someone please debunk this?’ Read about how our reporter grappled with writing about genetics and white supremacists.]

Instead of long-discounted proxies like skull circumference and family pedigrees, according to experts who track the far-right, today’s proponents of racial hierarchy are making their case by misinterpreting research on the human genome itself. And in debates that have largely been limited to ivory-tower forums, the scientists whose job is to mine humanity’s genetic variations for the collective good are grappling with how to respond.

“Studying human genetic diversity is easier in a society where diversity is clearly valued and celebrated — right now, that is very much on my mind,” said John Novembre, a University of Chicago evolutionary biologist who has taken to concluding his visiting seminars by illustrating how one of the field’s textbook examples of natural selection has been adopted for illiberal ends.

One slide Dr. Novembre has folded into his recent talks depicts a group of white nationalists chugging milk at a 2017 gathering to draw attention to a genetic trait known to be more common in white people than others — the ability to digest lactose as adults. It also shows a social media post from an account called “Enter The Milk Zone” with a map lifted from a scientific journal article on the trait’s evolutionary history.

In most of the world, the article explains, the gene that allows for the digestion of lactose switches off after childhood. But with the arrival of the first cattle herders in Europe some 5,000 years ago, a chance mutation that left it turned on provided enough of a nutritional leg up that nearly all of those who survived eventually carried it. In the post, the link is accompanied by a snippet of hate speech urging individuals of African ancestry to leave America. “If you can’t drink milk,” it says in part, “you have to go back.”