The scientist Richard Dawkins sparked controversy when he tweeted that, aside from the moral problems, eugenics would work “in practice.” While that remark is shocking, Dawkins is hardly alone in accepting the premise at the heart of eugenic science and population-control theory. Last year, a group of 11,000 scientists signed a statement urging population control to slow human exploitation of Earth’s fragile resources. With climate change finally a topic of urgent debate, some have argued that limiting population growth — if not eugenics — could be part of saving the planet.

The idea that people should reproduce less to preserve our shared resources is nothing new. It is an old idea with a violent history. When reformers have encouraged — or forced — women to have fewer children in the name of population control, it has been the most vulnerable people and those most likely to be deemed undesirable or unfit who have paid the price. While advocates for reproductive rights and green activists alike may call for support for greater individual bodily autonomy, they should be careful not to reinforce the dangerous, even eugenicist, forces behind encouraging population control, like those hinted at in Dawkins’s tweet.

Although the United States has not enacted an official, nationwide population policy, debates on population control have surfaced over the years across the political spectrum — involving leaders from President Richard M. Nixon to Vice President Al Gore. However, the dark underbelly of population control — from eugenics in the early 20th-century United States to mass murder during the Holocaust to compulsory sterilization in India in the 1970s and China’s one-child policy — has undermined serious conversation about global family planning or strategies to combat climate change, poverty and overpopulation by addressing population growth.

The English statistician Francis Galton, Charles Darwin’s cousin, coined the term eugenics in 1883 after studying the heritable qualities of human intelligence and ability. The eugenics movement gained momentum in early 20th-century America as, among other things, a way to explain genius and good character as well as criminality, bad social behavior and “feeblemindedness.” Eugenicists sought to improve the human population and its gene pool through encouraging “fit” individuals to procreate (positive eugenics) and discouraging or preventing the reproduction of the “unfit” (negative eugenics). This led to the forced sterilization of thousands of Americans and, in the case of Nazi Germany, the justification for murdering millions of people.