“Eugenics” (Greek for “well bred”) was given its name in 1883 by Darwin’s cousin Francis Galton, the creator of the IQ test. Galton gained widespread support for eugenics by arguing, theologically, that eugenics was a proper application of the Gospel parable of the talents, while also arguing, culturally, that Darwin’s idea of natural selection helped explain why white European men had conquered the world and were thus the most advanced examples of humanity. This intermingling of racism, science, philosophy, theology, and politics laid a terrible groundwork for mainstream scientific thought in the late-nineteenth and early-twentieth centuries. For Galton and most of the educated elite, the program of eugenics would allow humans to do intentionally what nature does randomly: favoring the most biologically capable, the “fittest,” and gradually ridding the world of the unfit. Between 1883 and 1939—the year World War II began—eugenic philosophies, theologies, and laws spread like wildfire.

Before the rise of Nazi Germany, the most potent application of eugenics was in the United States, whose ruling class held tightly to racism, xenophobia, and cultural progressivism. Eugenics in the United States included campaigns to encourage the reproduction of the fittest human specimens, celebrations of the fittest babies, and efforts to determine, via Galton’s IQ test and other measures, the “most fit humans.” But it also included forced-sterilization and anti-miscegenation laws, forced birth control, forced abortions, concentration camps, and unethical scientific experiments on black and other nonwhite communities.

Beyond the United States, eugenics played into the hands of powerful people with sinister agendas. In Canada and Mexico, anti-indigenous biases determined the nature of most eugenic laws. In South Africa, Tanzania, Namibia, Kenya, Rwanda, and Burundi, anti-black and anti-indigenous racism motivated both sterilization and anti-miscegenation laws, as well as death camps. In most of Europe, as well as Russia, China, Iran, Australia, and New Zealand, the eugenics movement channeled long-established hostility to Jews, Africans, indigenous peoples, women, and immigrants.

In all these countries, including the United States, people with disabilities and the poor were among the first to be sterilized, silenced, or killed. Thousands of scientific experiments were performed on people against their wills, and countless laws inspired by eugenics were passed in the name of scientific progress. The genocidal actions of Nazi Germany and all German-controlled countries were uniquely horrific in their implementation of eugenic ideas, but Hitler’s program was largely inspired by the language and laws of the American eugenics movement.

While eugenics spread so quickly because of its standing as an accepted application of a scientific theory, it’s important to remember that Christians played a large role in the dissemination of eugenics. Galton and many others used explicitly theological language to argue for eugenics from the beginning. As Christine Rosen writes in Preaching Eugenics, “one of the largest standing committees of the American Eugenics Society [in the first three decades of the twentieth century] was the Committee on Cooperation with Clergymen.” In fact, clergy of many religious traditions joined in the cause, writing, preaching, and lecturing widely in support of eugenics.

Anti-modernist Catholics were one notable exception to this. Together with fundamentalist Protestants, most Catholics opposed both evolution and eugenics. Eugenics was largely supported by moderate and liberal Christians who embraced science because they believed it was on the side of social progress. The same people who supported some variety of eugenics often championed progressive political causes. Such figures included Helen Keller, Winston Churchill, Teddy Roosevelt, and (as I’ve previously argued here) Pierre Teilhard de Chardin. Some eugenics supporters believed all peoples (though not necessarily all people) were equal (e.g., W.E.B. DuBois), but most believed that those of non-European descent were all inferior to whites.

In short, if you accepted Darwin’s evolutionary theory in the early twentieth century, you probably also supported eugenics. Pro-science progressives embraced both, while conservatives, including the Vatican, rejected both. Very few rejected one but not the other.