Today, though, the conversation has completely changed. There has been a frenzy of excitement around the possibilities of CRISPR-Cas9. The technology, which allows scientists to design proteins that unzip and replace chunks of DNA as they please, makes it possible to edit genes quickly and cheaply. Investors have poured hundreds of millions of dollars into the innovation, which seems to have endless possibilities: making crops more resilient to diseases, designing mosquitoes so they can’t carry malaria — maybe even eliminating diseases among humans by altering the genes we pass on.

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Scientists are confident that the technology could one day eliminate genetic disorders in humans. However, the research is still very young, and there are major ethical questions attached to editing human DNA that the emergence of CRISPR makes even more pressing: Wouldn’t editing out inheritable traits from the human population simply amount to eugenics? Could there be unanticipated negative consequences for future generations? How do you distinguish between negative “disorders” and valuable diversity?

The field of genetics has always had an uncomfortable link to eugenics: the science of improving people through controlled breeding. Centuries ago, people realized that desirable traits in farm animals could be passed down to their offspring. In the late 19th century, “social Darwinists” began to advocate for artificial selection among humans as well, often along racial terms. Such policies were enacted under fascist regimes during World War II, with the expressed goal of eliminating what were seen as negative traits from the human gene pool through genocide or sexual sterilization. The United States even had versions of these involuntary sterilization policies, implemented to protect the country’s “racial hygiene.”

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Today, the scientific community soundly condemns such atrocities, yet prominent biologists have long advocated for genetic engineering as a means of perfecting the human species. During the 1950s and ’60s, as postwar thinkers began uncoiling the mysteries of DNA, scientists began to suggest that people may one day be able to guide human evolution by altering the microscopic blueprints government laid out in our cells.

Nobel Prize-winning biologist Joshua Lederberg conceded that altering human DNA could possibly lead to eugenics of a sort, but he argued that it was substantially different from the genocidal eugenics committed by the Nazis. No living person would be eliminated from the gene pool — as eugenics often implies. Instead, society could guide human development by eliminating negative traits and encouraging desirable ones through genetic engineering. Evolutionary biologist J.B.S. Haldane called this “positive eugenics.”

At the time, though, there was no technology available to edit human DNA, so Lederberg viewed talking about guiding human evolution as “diversionary” to the true potential of genetics: research that could lead to medical gains. The question of eugenics remained largely marginal.

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Over the next few decades, genetic research would, in fact, produce milestone advancements in the medical field. DNA research has produced treatments for diabetes and potentially for Parkinson’s disease. CRISPR was, in fact, discovered not by scientists who wanted to edit the genome but by researchers studying genetic immunity among bacteria. Unexpectedly, CRISPR technology has led to a vast range of medical possibilities, from “three parent” children to the prevention of mitochondrial diseases.

Today, CRISPR has captured the fantasies of those who emphasize the high-flying possibilities of human-led evolution. Some look forward to “designer babies,” suggesting that altering children to have higher intelligence is inevitable for human progress. Others argue that we should engineer humans so they have a reduced impact on the environment.

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Of course, these proposals are still wildly unrealistic. But we’re no longer in an era where scientists can shrug off eugenicist rhetoric as too distant to worry about. This month, Britain became the first country to approve public funding for projects that edit the human genome. At the pace that CRISPR technology is advancing, it’s likely that the United States and other governments will want to follow suit. While 83 percent of the American public is solidly against editing genes for frivolous purposes such as increasing intelligence, about half of those asked were fine with the idea of doing so to treat diseases. The time to distinguish between negative eugenics and positive genetic intervention is now.

But how far are we willing to go? Ending truly debilitating diseases may be one thing, but what about conditions such as dwarfism? Current CRISPR research might lead to genetic treatments for autism. Given that the possibilities truly are endless, should we edit out traits that many people have come to accept and celebrate? Isn’t there a moral, social and physical advantage in allowing diversity to flourish within the human gene pool?

In the end, where we draw the line will be a political question. The scientific community has already begun this discussion, but it’s not unreasonable to expect a more involved debate in the near future — one in which the general public will have a greater say in how science will proceed.