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Chris Mason is a man in a hurry.

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“Sometimes walking from the subway to the lab takes too long, so I’ll start running,” he told me over breakfast at a bistro near his home in Brooklyn on a crisp autumn morning. “Just so I can get there faster. Not because I’m late for a meeting, just because it’s taking too long to walk … I’m the only one I know who runs to work to get there faster.”

Mason is a professor of physiology and biophysics at Weill Cornell Medicine. At least that’s his official title. He seems to be working on a hundred different projects all at once, ranging from tracking changes in the virus that causes COVID-19 to helping corals adapt to climate change.

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The previous day, I had visited his research group on the Upper East Side. The Mason Lab occupied four separate laboratories across three buildings and was still growing. Although they were pursuing a wide range of projects, a major focus of their work was on how the human genome and microbiome are affected by spaceflight. What Mason and his researchers know for sure is that settlement of space will lead to major changes to our biology, one way or another.

If we let these changes unfold naturally, evolution will take its course, and people on Mars will gradually become better adapted to the conditions there through mutation and natural selection. Founder effects and genetic drift will cause random changes in Martians and reduce their genetic diversity. Enforced quarantines due to the risk of spreading infectious diseases could accelerate the speciation process. But these natural evolutionary processes will be relatively slow and, to put it mildly, quite unpleasant. What if we could accelerate the process of adaptation and minimize the human suffering that it would otherwise entail?

Mason thought that we could—and he laid out his argument in detail. “One possibility is we simply allow evolution to gradually select for characteristics required to survive on these new planets,” he wrote in his book, The Next 500 Years. “This is basically the ‘sink or swim’ approach to life’s survival, except with no lifeguards and bricks tied to your feet.”

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However, there is an alternative: “Our second option to enable Earth’s life to live on other planets is to preemptively direct this genetic process, so that the life we send is already capable of surviving in its new home. More complex, yes—but also more humane.”

“Genes from all organisms will become a playground for creating and making new functions in human cells.”

The basic idea of acquiring new abilities by taking DNA from one organism and putting it into another has existed since the 1970s. In 1972, biochemist Paul Berg became the first person to do this when he copied a short piece of DNA from a virus that attacks bacteria into another kind of virus that attacks monkeys. The following year, Herbert Boyer and Stanley Cohen applied this “gene splicing” technique to insert genes from one species of bacteria into another. They found that the inserted gene persisted in subsequent generations as the bacteria divided. Going one step further, they then spliced genes from a frog into a bacterium, and found that the frog genes became a permanent addition to the bacterium’s genome.

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This was the dawn of a revolution in biotechnology. Recombinant DNA—meaning DNA copied from one organism and pasted into another—could be used for an incredible number of things, from producing life-saving medications like insulin to more whimsical applications like making glow-in-the-dark cats and goldfish. But it was also the beginning of an era in which humans could directly control the evolution of any species by manipulating their DNA. Mason saw the potential to take genes from organisms naturally well-adapted to harsh conditions and insert them into human cells to help prepare people for the hazards beyond Earth.

One candidate for such a hardy creature is the water bear, or tardigrade. Tardigrades are distant relatives of insects but have a unique appearance. They are barely visible to the naked eye, but under a microscope, they look like tiny gummy bears with eight chubby little legs and mouths shaped like nozzles. They thrive in moisture, but their adaptability allows them to live almost anywhere, from the sea to the soil in your backyard. One of the ways they are able to live in such a wide range of habitats is by tolerating long periods of harsh conditions—say, a drought—by essentially shriveling up. In their dehydrated state, they are almost invincible, which is what has drawn the attention of biologists interested in life in outer space.

In 2016, a team of Japanese researchers led by Takekazu Kunieda and Atsushi Toyoda sequenced the genome of one particularly hardy species of tardigrade. In the process, they discovered that tardigrades produce a protein that helps them survive in a dehydrated state. They named the protein “damage suppressor,” abbreviated Dsup. The researchers then took a major leap: They extracted the Dsup gene from the tardigrade genome and temporarily spliced it into human cells. To be clear, the human cells were growing in a laboratory, not a human body. Nevertheless, they found that when the tardigrade gene was inserted, human cells could produce Dsup. And—most significantly—when they exposed the human cells making Dsup to radiation in the form of X-rays, the cells were less damaged and better able to grow than normal human cells.

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Mason’s lab began working to further improve human cells’ ability to withstand the harsh conditions of space by splicing in genes from tardigrades and other organisms that survive in extreme environments. He sees this as the beginning of an era in which human cells can be endowed with a great variety of abilities. He predicts that by the year 2040, “genes from all organisms will become a playground for creating and making new functions in human cells.”

The notion that the diversity of life on Earth represents a genetic “playground” for us to draw from seems exciting, but it is also fraught with risks, ranging from the biological to the ethical.

Indeed, after the first demonstrations of gene splicing, researchers quickly recognized the double-edged-sword nature of the new technology. A voluntary moratorium was called on the use of recombinant DNA. A conference was held in 1975 at Asilomar Beach in California, where many leading researchers came together to develop guidelines for its use. The meeting, which has variously been called “Woodstock for molecular biology” and “the Pandora’s box conference,” was in part an attempt by researchers to come up with their own limits on the use of genetic technology in the hopes that doing so would prevent government regulations. After four days of meetings, the researchers agreed to lift their own self-imposed moratorium on the use of recombinant DNA, albeit with some guardrails intended to prevent what they saw as its most potentially dangerous uses.

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Is it ethical to make decisions that will directly affect future generations?

It seemed plausible that some genetic diseases could be cured with recombinant DNA by swapping out the section of DNA responsible for the condition with DNA from a healthy donor.

The first success came in 1990 with a child named Ashanthi DeSilva. At the age of 2, she had been diagnosed with SCID—the same condition as the “bubble boy,” David Vetter, that results in a nonfunctional adaptive immune system. In 1990, when DeSilva was 4 years old, she was given a fully approved experimental gene therapy to replace the cells in her bone marrow that cause the condition. It worked. With the modified genes, DeSilva’s immune system began functioning well enough for her to go outside, attend school with other kids, and lead a normal life.

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Another major breakthrough came with the discovery of a way to edit DNA directly: CRISPR.

By 2023, the first two CRISPR-based treatments, which use molecular scissors to precisely modify specific parts of the genome, were approved in the United States—one for sickle cell disease and another for the blood disorder beta-thalassemia.

Read more: “The Martians Are Coming—and They’re Human”

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There is a catch, however. While the hope is that patients receiving CRISPR treatments will be fully rid of their diseases, the gene-editing approaches approved so far would not prevent any of their children from inheriting their parents’ diseases. The genetic changes are made only to DNA in somatic cells—the cells of the body that are not involved in making sperm or eggs. For their children to be cured, they would need to undergo the same treatment as their parents. The same would be true of every subsequent generation.

The alternative would be to make edits to cells in a way that affects not only somatic cells but also germline cells—those that become eggs, sperm, and eventually embryos and then babies. Germline gene editing is possible, although it crosses a line that some believe should not be crossed. The reason is that any edits made to germline cells will affect all the descendants of the individual receiving the treatment, for countless generations. This raises new types of ethical questions. It is one thing to perform a procedure on a living person, who can be educated about the potential risks and benefits and who can give their informed consent. Is it ethical to make decisions that will directly affect future generations who will not have any choice in the matter?

Changing the germline means we are, whether we realize it or not, controlling the future of evolution. Yet while the techniques of gene editing are new, the idea that we humans can guide evolution is not. As Mason pointed out, we have been doing so for millennia through the practice of selective breeding in agriculture and the domestication of animals.

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“While controlling the evolution of the past, present, and future seems scary and wrought with incredible hubris, the reality is that we already have been engineering and modifying species and the environment around us, except previously we were doing so by accident with no foresight,” Mason wrote. “Now, finally it can be done with a sense of responsibility and purpose.”

Yet the idea of purposefully controlling the evolution of our own species has a dark history.

The atrocities committed in the name of eugenics in the first half of the 20th century were based not only on prejudiced and racist views, but also on flawed science. We now know that there is little, if any, genetic basis for the traits that proponents of eugenics sought to control. Still, any discussion of manipulating the future of human evolution must consider the flaws inherent in previous attempts to do so, as well as the ways those efforts were perverted and abused.

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Questions about the ethical use of gene editing become more complex when considering humans on other planets. Would it be ethical to change a gene to make a person traveling to Mars better able to tolerate lower gravity or higher radiation? What about for a child born on Mars? Could genome editing make it easier to allow people to move safely between planets, for example, by altering their immune systems?

Mason sees gene editing in the context of space settlement as a moral imperative. “Sending any Earth-evolved organism to another planet would result in almost certain death, which represents the sad, evolutionary ‘good luck’ plan,” he wrote. “To save life, we will need to engineer it.”

Mason’s reasoning is based on an ethical philosophy he calls “deontogenics.” According to this way of thinking, as a species that is aware of the possibility of our own extinction and that of other species, we have an ethical obligation to try to prevent that from happening. “Any act that consciously preserves the existence of life’s molecules … across time is ethical. Anything that does not is unethical,” Mason wrote.

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With this framework in mind, Mason and his research team are pressing forward on genetically engineering human cells to make them better adapted for conditions beyond Earth. They have had some success with getting human cells to produce the Dsup protein that helps tardigrades survive in space. So far, their work involves only human cells being grown in a lab, but he hopes that will soon change. “I’d say human trials are 10 years away,” he told me.

A list of other genes that could be modified to help people to deal with life on Mars and elsewhere has been identified by George Church, Mason, and colleagues at Harvard’s Consortium for Space Genetics. They include genes that influence bone density, muscle tone, radiation resistance, and even pain tolerance. In part, the list comes from studies of existing genetic variation within people alive today. It also comes from organisms capable of living in extreme environments, like tardigrades and others.

Synthetic human genomes might be possible.

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One particularly hardy species of bacteria was first discovered in the 1950s in a can of meat that had been exposed to a whopping dose of 5 million millisieverts of radiation. The goal was to determine whether radiation could be used to sterilize canned foods and make them safe to eat. Yet the bacteria were still alive. The researchers identified them as belonging to the genus Deinococcus and named the species radiodurans in reference to their remarkable ability to endure such high radiation exposure. Even tougher bacteria, like the appropriately named Thermococcus gammatolerans, have been found in the water used to cool nuclear power plants. The genetic basis of these species’ abilities to withstand radiation is being investigated by Mason and his colleagues for their potential use in engineering life beyond Earth.

Another approach Mason is researching is to genetically engineer genes in bacteria and other microbes in our microbiome to produce useful products, including Dsup. This way, no changes to human cells would be required, but people might still reap the benefits if the substances produced by microbes are active within the human body. They already have some microbes in the lab that seem capable, he told me, but so far, they have not tested whether the microbes would work the same way when living in humans.

“It’s still a few years before we do a trial like that,” Mason said.

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So, we can edit our genes or those of our microbial partners. But there is yet another way that genetic technology may facilitate the human migration into space: by creating genes that do not yet exist.

In the first decades of the 21st century, the field of synthetic biology emerged with the goal of creating new functions for living things using genetic tools. Scientists at the J. Craig Venter Institute created the first complete synthetic genome of a simple organism, a type of bacteria, in 2010. Work has since been underway to create synthetic genomes for more complex organisms. Eventually, synthetic human genomes might be possible.

One idea, suggested to me by biologist Tiffany Vora, is to create synthetic portions of a human genome. For example, while humans normally have 23 pairs of chromosomes, one or more new chromosomes could be added to augment our existing genome. “The idea that we’re going to find all the mutations we need in Earth’s situations—I don’t believe it, because we’re fundamentally looking for a non-Earth context,” Vora told me. The advantage of this approach is that the existing genome could be left untouched. “If you can make really long artificial chromosomes, then you don’t have to change the person—you just give them a patch, essentially.”

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This raises the possibility that future humans with additional synthetic chromosomes may be genetically incompatible with people without them. If used for space settlement, this could be yet another force driving a wedge between humans from Earth and humans living elsewhere. Adapting to life in space may require genetic engineering, but engineering people for space might also contribute to a split in humanity. At some point, people may have to choose between prioritizing adaptation for life on other planets and maintaining human beings as a single species. It might not be possible to achieve both.

If humans—in one form or another—are going to ever leave our solar system, Mars will be an important stepping stone. On Mars, humanity will learn to create and sustain new settlements. Mason thinks of this first, cautious step in humanity’s lifetime as being like going to college. “Leaving the house you grew up in, traveling just out of the reach of your parent’s ability to instantly help you, and testing your limits, boundaries, and potential—all while having fun, learning a lot, and likely getting into trouble,” he wrote about our first settlements on Mars.

If we do manage to spread out and survive on planets scattered across our solar system and others, we should expect to evolve, adapt, and speciate everywhere we go. Like tortoises and finches on Earthly islands, the conditions on each of the cosmic islands will influence how the people there will evolve. Some may choose to let the natural forces of mutation, natural selection, and genetic drift determine how they change. Others may decide to take matters into their own hands, using technology to guide the process.

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To ensure we are ready, Chris Mason is moving forward with his work on engineering the genes of living things—humans and microbes—for their future in space. Despite often thinking in timescales that involve hundreds, millions, or even billions of years, he sees his work as urgent.

“I wake up almost every morning and think about the sun engulfing the Earth,” he told me. “It’s almost the first thought in my mind. It’s a cosmological fact. I see the sun every morning. It’s still there, and it’s only going to get bigger … I only have so much time … I’ll have another, say, 30 years, 40 years, maybe, of productive work I could do. Maybe 50, at most. But that’s it. I don’t have 500 years … I want to do as much as I can.”

Suddenly, his fast walking made a little more sense.

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This excerpt is reprinted with permission from MIT Press Reader. It is adapted from Becoming Martian.

Lead image: Anton Vierietin / Shutterstock

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What Do You Get When You Cross a Tardigrade with a Space Pioneer?