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.

The population movement of the 20th century has shied from that legacy and focused on how family planning could be used to minimize damage to the environment and human life. Although these efforts have bolstered the cause of racist eugenics, they also had an active role in advancing women’s rights. Biologist and Zero Population Growth (ZPG) founder Paul Ehrlich attempted to educate Americans about the importance of having smaller families for the sake of the environment and human quality of life. Beginning in the late 1960s, ZPG expanded its activism, arguing that overpopulation contributed to virtually all of the world’s modern ills: traffic, pollution, overcrowding and poverty, among others. Yet, not coincidentally, Ehrlich’s work initially focused on poor cities in the global south, such as the Indian state of Delhi, as the problem and the real cause for panic — rather than the consumption rates of wealthy, majority-white countries with much higher populations and rates of consumption.

The link between population control and the darker uses of eugenics was never eliminated, which led to inhumane solutions across the globe. The problem? Many population-control advocates focused on coercive population campaigns that targeted the most powerless people.

In the 1970s, China’s one-child policy mandated contraceptive devices, abortion and sterilization for women who became pregnant with a second child. (There were exceptions, such as if the woman’s first child was a girl or born with a disability.) Although this policy ended a few years ago, it has resulted in persistent low fertility rates, a “profoundly skewed sex ratio” and, some researchers say, significantly higher crime rates in China.

In India, a policy of forced sterilization during the 1970s also took the goal of curbing the population to the extreme, depriving citizens of the freedom and right to engage in voluntary family planning, mainly targeting poor men and some women. Even into the ’60s and ’70s, many poor women of color were subjected to forced sterilizations in the United States, often while seeking another type of surgery or after childbirth. Like eugenics, these compulsory initiatives sought to limit the reproductive rights of great numbers of men and women for the “health” of the nation.

Even in the Zero Population Growth movement, anti-immigrant, pro-eugenics figures such as John Tanton found a platform for using concerns about population to advance racism, bigotry and nativism, as well as an “us” vs. “them” mentality. Tanton and others from the population movement helped pave the way for the anti-immigrant, nationalist rhetoric of the Trump administration.

Such concerns about population fueled government-mandated solutions that undermined voluntary individual choice. Although some of ZPG’s members did advocate compulsory population policy, others said that giving women greater choice — through promoting reproductive rights and challenging the country’s deep-seated pronatalism — was the best, most humane solution to population growth. They may provide a blueprint for those worried about overpopulation today.

As the largest grass-roots population movement in the United States, coercive and racialized approaches to population are a troubling part of the history of ZPG. But many of its earliest and youngest members did not support coercive measures to control the population. In fact, many believed strongly in sexual liberation and advancing women’s reproductive rights as part of their environmentalist goals. Here, providing education and resources was key.

To address population growth, many grass-roots activists took the education of ordinary Americans into their own hands, distributing literature and leaflets, fighting legal battles alongside frustrated women who sought sterilization and being an active force in the abortion rights movement. They not only promoted birth control, but also held contests for free vasectomies and prescriptions for the pill. With catchy bumper sticker slogans such as “The Population Bomb Is Everyone’s Baby” and “Control Your Local Stork,” many members of ZPG emphasized the importance of population activism at local levels, highlighting the positive changes people could make for the world. Focusing on each person’s responsibility and action, in part, challenged the pessimistic, declensionist message of the modern environmentalist movement.

For example, from 1971 to 1973, ZPG, along with the Association for Voluntary Sterilization (AVS) and the American Civil Liberties Union (ACLU), ran “Operation Lawsuit,” which provided resources and advice to men and women seeking voluntary permanent sterilization. ZPG members fought to give more Americans access to birth control, abortion, sterilization, pregnancy prevention and comprehensive sex education. In doing so, they maintained, parenthood would become more deliberate and voluntary and thus, fewer people would be born. But ZPG also advocated for wider changes to American cultural and social norms, which were largely pronatalist, pushing back against the idea that motherhood was the be-all and end-all of womanhood. Some labeled these norms “coercive pronatalism,” citing the problem of accidental teen pregnancy, attacks on abortion rights and the minimum-age requirements that hospitals placed on women who wanted to be sterilized. Addressing women’s inequalities, they said, would inevitably drive down population growth.

Unfortunately, while these efforts helped advance the cause of women’s rights, they also distracted from the larger drivers of climate change, such as high fossil-fuel consumption. (In fact, much of the support for the population movement, including its racist, anti-immigrant leanings, has been funded by powerful and wealthy people and corporations profiting off the consumption of fossil-fuel energy.)

Today, we are seeing a resurgence of individual efforts to address environmental problems. We should praise those who seek to tackle climate change by choosing to have fewer children, but we should also be careful not to reignite the darker forces behind population control or lose sight of the most harmful sources of environmental degradation. And, as history demonstrates, any efforts to curb the population must be voluntary. Rather than focusing on controlling global fertility rates, we need to support and protect policies, ideas and activism that foster greater reproductive choice, resources and education for everyone.