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Scientists added human brain genes to monkeys. Yes, it’s as scary as it sounds.

Some are calling the Chinese experiment “an ethical nightmare.”

A one-month-old macaque monkey in China.
A one-month-old macaque monkey in China.
Barcroft Media via Getty Images
Sigal Samuel is a senior reporter for Vox’s Future Perfect and co-host of the Future Perfect podcast. She writes primarily about the future of consciousness, tracking advances in artificial intelligence and neuroscience and their staggering ethical implications. Before joining Vox, Sigal was the religion editor at the Atlantic.

Scientists in China have created a new kind of monkey. It’s got a human brain gene. And that just might make its intelligence a little bit more like ours.

That, in turn, makes its fate — and its very existence — very ethically fraught.

In a study published last month in Beijing’s National Science Review journal, researchers took human copies of the MCPH1 gene, which is believed to play an important role in our brain development, and introduced it into monkey embryos by means of a virus that carried the gene.

Of the 11 transgenic macaque monkeys they generated, six died. The five survivors went through a series of tests, including MRI brain scans and memory tests. It turned out they didn’t have bigger brains than a control group of macaques, but they did perform better on short-term memory tasks. Their brains also developed over a longer period of time, which is typical of human brains.

Although the sample size was very small, the scientists excitedly described the study as “the first attempt to experimentally interrogate the genetic basis of human brain origin using a transgenic monkey model.” In other words, part of the point of the study was to help tackle a question about evolution: How did we humans develop our unique brand of intelligence, which has allowed us to innovate in ways other primates can’t?

The Chinese researchers suspect the MCPH1 gene is part of the answer. But they’re not stopping there. One of them, Bing Su, a geneticist at the Kunming Institute of Zoology, told MIT Technology Review that he’s already testing other genes involved in brain evolution:

One that he has his eye on is SRGAP2C, a DNA variant that arose about two million years ago, just when Australopithecus was ceding the African savannah to early humans. That gene has been dubbed the “humanity switch” and the “missing genetic link” for its likely role in the emergence of human intelligence. Su says he’s been adding it to monkeys, but that it’s too soon to say what the results are.

Su has also had his eye on another human gene, FOXP2, which is believed to have graced us with our language abilities. Pondering the possibility of adding that gene to monkeys, Su told Nature in 2016, “I don’t think the monkey will all of a sudden start speaking, but will have some behavioral change.” He would not be breaking any laws. (In the US, scientists have created human-animals hybrids in an attempt to grow human organs for medical transplants — for example, by injecting human cells into a pig embryo and a sheep embryo — but such studies are not eligible for public funding.)

Su’s prediction that his tinkering would cause behavioral change raises a slippery slope concern: If we deem it acceptable to make an animal slightly more human-like, we may end up normalizing that process and find ourselves generating animals that resemble humans to ever greater degrees.

Changing monkeys’ behavior and intelligence raises major ethical issues

If you make primates smarter and more human-like, you’re not doing them any favors — not least if you’re going to then keep them locked up in a lab. In the words of University of Colorado bioethicist Jacqueline Glover, “To humanize them is to cause harm. Where would they live and what would they do? Do not create a being that can’t have a meaningful life in any context.”

In a 2010 paper titled “The ethics of using transgenic non-human primates to study what makes us human,” Glover and her co-authors wrote that it’s unethical to add human brain genes to apes (such as chimpanzees). Su told MIT Tech Review he agrees that’s out of bounds given how similar apes are to humans — after all, chimps and humans share a recent common ancestor and 98 percent of DNA.

But monkeys aren’t apes. The last time they shared an ancestor with us was 25 million years ago, which Su thinks changes the ethical calculus. “Although their genome is close to ours, there are also tens of millions of differences,” he said, adding that for monkeys to become meaningfully un-monkey-like would be “impossible by introducing only a few human genes.”

That kind of justification is abhorrent to Barbara J. King, author of How Animals Grieve and an emerita professor of anthropology at the College of William and Mary. In an email, she called Su’s experiment “an ethical nightmare,” writing: “More of the genetically altered monkeys — six — died than lived, so right off the bat we see that the procedure is often lethal. Regarding the five survivors, what kind of lives will they have going forward, altered as they are and confined to an experimental laboratory?”

A macaque mother with her baby in Guiyang, China.
A macaque mother with her baby in Guiyang, China.
Lintao Zhang/Getty Images

King also suggested a cost-benefit analysis of Su’s study does not shake out in his favor. “In the wild, macaques live in matrilines, centered around groups of related females with close social ties; they explore their world with intelligence and curiosity. What right do we have to subject these primates to grotesque procedures of this sort?” she wrote. “The costs are terribly high and the benefits to humanity approach zero; there’s growing recognition that animal models simply don’t work well to study complex human processes.”

Primates have often been used in studies aimed at understanding how various diseases develop and how we can treat them in humans. Yet it’s important to note that there’s a difference between giving a monkey a disease and giving a monkey more human-like intelligence. Obviously, if you inflict a disease on an animal, you’re causing that animal harm. But you are not changing the fundamental nature of what it means to be that animal.

Adding human brain genes to a monkey, however, stands to fundamentally change the way the monkey perceives and interacts with reality. So, even if you think it’s morally acceptable to experiment on monkeys in the name of better treating disease in humans, it’s still a leap from that to Su’s experiment. After all, the very premise of that experiment is that the monkeys may end up more human-like as a result of it.

Su is right to note that there are “tens of millions of differences” between humans and monkeys. But his transgenic study is definitionally aimed at eliminating a few of those differences. After how many eliminated differences does a monkey shade into a human being? There’s no clear answer to that question.

China is particularly hospitable to primate research

It’s hard to imagine a study like Su’s ever getting the green light in the US, where primate research has come under increasing scrutiny, thanks in part to the work of animal rights advocates. But China is much more open to this kind of research. The country has vast breeding facilities for monkeys, tens of thousands of which it exports each year.

This picture released by the Chinese Academy of Sciences Institute of Neuroscience shows five cloned macaques at a research institution in Shanghai. 
This picture released by the Chinese Academy of Sciences Institute of Neuroscience shows five cloned macaques at a research institution in Shanghai.
STR/AFP/Getty Images

When it comes to studying monkeys, a researcher gets much more bang for their buck in China, as the Atlantic’s Sarah Zhang reported last year:

A standard monkey in China costs about $1,500, compared to roughly $6,000 in the United States. The daily costs of food and care are an order of magnitude lower as well.

In the past few years, China has seen a miniature explosion of genetic engineering in monkeys. In Kunming, Shanghai, and Guangzhou, scientists have created monkeys engineered to show signs of Parkinson’s, Duchenne muscular dystrophy, autism, and more.

Because of the relative ease of conducting primate research there, some researchers regularly travel from the US to China for scientific work on monkeys. As Zhang pointed out, researchers at Emory University recently collaborated with scientists in China who work on genetically modified monkeys. And Su’s study involved University of North Carolina computer scientist Martin Styner. Styner, who told MIT Tech Review that his participation was minimal, said he considered pulling his name from the study and has come to believe such research is not “a good direction.”

Although the US is not green-lighting studies like Su’s, American universities that collaborate with Chinese scientists on such studies may still be complicit in any ethical harm they cause.

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