A whole new thing that could end the world

We’re all inured to sensationalist headlines about some disaster or another on the horizon. So I don’t blame anyone who was exhausted when they saw last month that dozens of scientists were warning in the journal Science that mirror bacteria could bring about a catastrophic ecosystem collapse and even mass extinction.

After all, we already have looming threats like H5N1 to worry about, and more generally we live in an age that, as Adam Kirsch put it recently in The Atlantic, feels like “apocalypse, constantly.” The mirror bacteria news hit the same week we were told that a widely read study about how our black spatulas were killing us was really just the result of a math error. It can be hard to tell which concerns are deathly serious and which are just headlines that will be forgotten a month later.

But having done a lot more reading about the mirror bacteria situation, I’m here with bad news: It’s real, and it’s really serious.

More than 35 scientists, including leading researchers across half a dozen different fields, came together in a December technical report to argue that ongoing work on mirror bacteria could trigger a mass extinction. The catastrophe it warns about is plausible, if mind-bending.

And it’s not one of those situations where the skeptics are coming from outside the field: Many of the leading scientists who worked to invent mirror life have now become convinced such work would be incredibly dangerous. In fact it’s one of the rare cases where experts have become more concerned as they’ve learned more, instead of less so.

But there’s also good news: Now that we are aware of the risk, catastrophe shouldn’t happen by accident. At this point, mirror life is mostly theoretical — it would take decades of work to actually create it. So as scientists come to look more closely at the risks, they can bring about a stop to this work, with very little cost to other essential research.

And with scientists from across many disciplines expressing their concern, there’s a good chance that we can just agree, as a world, to do the right thing and just not go there. Which is ideally how we should be handling new existential risks.

Think about the letter R, and its mirror image, the letter Я. No matter how much you spin the letter R on a two-dimensional page, you’ll never get an Я. If you build a protein meant to link up to an R, a Я won’t fit, and a molecule will turn out differently if it’s using an R or a Я as a backbone.

That’s the core concept behind mirror life, though in three rather than two dimensions. The amino acids that compose the proteins that make up all life on Earth can form from atoms in two different mirrored ways, colloquially “left”- and “right”-handed forms. But while the molecules are around in both forms, all life on Earth builds proteins only out of left-handed amino acids (and most other biomolecules, like DNA, also come with a “handedness” — that’s why the spiral helix of DNA always goes one direction.)

This poses a tantalizing scientific puzzle: Couldn’t you, in principle, build “mirror life” — life made out of the right-handed amino acids? It would be an enormous engineering project, involving work we don’t yet know how to do.

But in principle, it ought to be possible. We have already built mirror proteins, and mirror enzymes that can read mirror genes.

What could possibly go wrong?

The question is what would happen after you succeeded in building mirror life.

At first it was assumed that mirror bacteria would be effectively harmless, because they can’t digest most of the “normal-handed” molecules that make up all existing life. Sure, they could eat simple nutrients, which do not have the “handedness” property. But would that be enough to let them multiply and spread?

Many scientists initially assumed that it wouldn’t be, meaning that mirror life would be safely self-limiting, unable to spread too far because it would be unable to digest the rest of life, human beings very much included.

But as they studied the possibility further, experts became worried that this wasn’t true. “Unlike previous discussions of mirror life, we also realized that generalist heterotroph mirror bacteria might find a range of nutrients in animal hosts and the environment and thus would not be intrinsically biocontained,” the Science report found.

So mirror bacteria would be able to find enough to eat after all. Even worse, existing life would struggle to eat them. That means that creating mirror bacteria could be kind of like introducing an invasive species to an ecosystem (in this case, the entire planet) where it doesn’t have any predators.

Without anything initially evolved to eat or counter it, it could probably spread rapidly. Invasive species can be very hard to eradicate, even if they don’t reach very high populations. Mirror bacteria might well be like this: a new species of globally distributed environmental bacteria, alongside the multitude of existing ones.

But how catastrophic would the introduction of this new invasive species be? Humans (and other animals and plants) are exposed to environmental bacteria all the time, and these aren’t usually an issue unless, for example, you have a damaged immune system.

So a team of immunologists worked on the question of whether our immune system would respond appropriately to an invasion by mirror bacteria. Worryingly, they concluded that it probably would not.

While some of our immune defenses function without any specific targeting of a particular pathogen, many of them only work by locking onto the invading pathogen — which we wouldn’t be able to do for mirror bacteria. And the scientists didn’t just find that it might make humans sick. For the exact same reason, it might make everything else sick — every animal, even plants might be vulnerable (though there would be substantial variation in exactly how susceptible any species would be).

The result, according to the December report in Science, could be terrifying.

“We cannot rule out a scenario in which a mirror bacterium acts as an invasive species across many ecosystems, causing pervasive lethal infections in a substantial fraction of plant and animal species, including humans.,” the authors found, saying a plausible result was “unprecedented and irreversible harm.”

“It is hard to overstate how severe these risks could be,” immunologist Ruslan Medzhitov, one of the co-authors of the technical report, warned in a statement sent to me. “Living in an area contaminated with mirror bacteria could be similar to living with severe immunodeficiencies: Any exposure to contaminated dust or soil could be fatal.”

“We’re not going to do it”

To be clear, there were plenty of good reasons to consider making mirror life. “It’s inherently incredibly cool,” Kate Adamala, a synthetic biologist at the University of Minnesota, told the New York Times, of the effort to make mirror bacteria. “If we made a mirror cell, we would have made a second tree of life.”

Indeed Adamala and three other scientific colleagues are the recipients of a 2019 grant in which they explained that they “seek to design, construct, and safely deploy synthetic mirror cells.” But as they looked into it more, through collaboration on the 299-page technical report, she and her colleagues became convinced that it just wasn’t worth it: All four have now joined the call in Science for work to be halted. “We’re saying, ‘We’re not going to do it,’” Adamala told the Times.

The US government, which funded Adamala and her colleagues’ work toward building mirror life, is also adapting in response to this warning.

“We appreciate the efforts of these scientists to identify and assess potential future risks of this type of synthetic organism, … Advances in the life sciences and associated technologies now empower scientists in ways that were barely imaginable just a few decades ago,” a spokesperson for the White House Office of Science and Technology Policy told me.

“These advances have remarkable potential for benefit and, as these scientists have made clear, also the potential for causing significant harm. Given the potential risks, we will work with and across the global research community to avoid and mitigate risk while protecting the potential benefits of research in other applications of synthetic biology. The U.S. government is beginning a deliberative process to review scientific assessments on the implications of mirror life and, as appropriate, develop or revise relevant federal biosafety policy.”

For that reason, I think this can be read not as a doom-and-gloom headline to start your year on, but as a hopeful story. An enormous number of talented people across different relevant disciplines came together and tried to figure out if there was a problem. They figured out that there was, and changed their course.

It’s too early to declare victory, of course. But if it’s a story of a looming challenge, it’s also a story of people stepping up to it — well before any catastrophe might ensue.

A version of this story originally appeared in the Future Perfect newsletter. Sign up here!