It could revolutionize human health — or it could spell our doom. It really depends on who you ask. I'm not talking about potentially risky biodefense lab research, but something that doesn't yet exist: mirror life.
Here's a refresher on normal biology: the cells in our bodies are composed of the building blocks of life. Nucleotides and sugars make up our DNA, which provides the blueprint for cells and codes for proteins that carry out key biological functions. In all of life, these biomolecules have a specific "handedness." (Bear with me here.)
A mirror image is possible, the way your left and right hands are mirror images of each other. But mirror life can't evolve from existing life in nature. If it eventually emerges, it's because we've created it.
As my former colleague Kelsey Piper explained back in January, mirror life could represent a whole new way that the world could end.
We're at least decades away from being able to create entire mirror cells — that includes bacteria. The technologies that would allow us to do so aren't yet up to the task. But we've encountered mirror biomolecules like right-handed amino acids in nature, and scientists have synthesized mirror enzymes capable of reading mirror genes. With the power of chemistry, researchers have created mirror proteins.
These mirror biomolecules are the building blocks of mirror life, but they are not mirror life itself. This distinction is really important, and not only because I'm being pedantic.
A paper published in Science last year made dramatic headlines after its authors laid out potential catastrophic risks of mirror life. Such risks include the possibility that mirror bacteria would evade our immune systems and lack natural predators, replicating to the point that they threaten to outcompete normal life. The authors concluded that "in the absence of compelling evidence for reassurance, our view is that mirror bacteria and other mirror organisms should not be created."
So if those are the risks, then we definitely shouldn't pursue the creation of mirror life. Right?
Well, only if we accept that those are the risks.
Something that's gotten a bit lost in the noise of media coverage is that the 35+ authors — who hail from fields as diverse as ecology, immunology, and synthetic biology — want mirror biomolecule research to continue. Nearly everyone agrees on that, because mirror biomolecules can offer immense benefits for developing new therapeutics, diagnostics, and studying the biochemistry of life without making new life itself.
The (brief) argument against mirror life
But first, let's get into why the idea of mirror life is so frightening.
Kate Adamala, a biochemist building synthetic cells at the University of Minnesota and the lead author of the Science paper, received a 2019 grant to develop and deploy mirror cells. Upon looking into it further, she decided that the risks far outweighed the benefits, and called for the work to be halted.
"Mirror molecules are safe to make, because unlike mirror bacteria, the molecules don't replicate, so they don't pose any risks of spreading uncontrollably," Adamala told me over email. One of her chief concerns is that normal cells may be unable to recognize mirror cells, because many of our immune mechanisms are based on chirality, or handedness. This could allow mirror cells to "grow unrestrained by the immune system and environmental predators" that keep normal cells in check.
Other risks include:
- The collapse of entire ecosystems
- The inability to develop robust medical countermeasures
- The possibility that mirror bacteria would be completely resistant to predation by other microbes that prey on bacteria and keep their population under control
Fun stuff!
"It's hard to overstate how severe these risks could be," Ruslan Medzhitov, an immunologist at Yale University and one of the paper's co-authors, told Science News. "If mirror bacteria were to spread through infected animals and plants, much of the planet's many environments could be contaminated. …Any exposure to contaminated dust or soil could be fatal."
We could see a mass extinction event, an existential threat to multicellular life as we know it. Effective biocontainment, the researchers argue, would be incredibly difficult. If you have the time, it's worth reading the 299-page technical report that explains how the study authors came to their conclusions.
The case for mirror life
That said, mirror life could offer real benefits. Mirror therapeutics, which wouldn't be recognized by our digestive enzymes, have the potential to last a lot longer in our bodies, opening up new possibilities for the treatment of chronic disease. Right now, we create mirror therapeutics chemically, putting them together atom by atom. Mirror bacteria could do this for us, and at a much greater speed, allowing us to produce mirror therapeutics en masse.
Synthetic biology and synthetic chemistry are relatively small fields, and mirror biology is even smaller. The declarations of a scientific consensus around mirror life may be premature, but a growing number of voices are getting involved in discussions on the possibility.
I want to make it very clear that right now, mirror life is only a possibility. And it might be more distant than we think. David Perrin, a synthetic chemist at the University of British Columbia, told me over email that science is nowhere close to creating a living mirror cell.
He is also skeptical that mirror bacteria would be toxic to normal life, and believes our immune systems would likely be able to neutralize them after all. Immune responses are complex, and not all rely on handedness.
The scale of the threat is unclear, because mirror organisms might be hopelessly outcompeted by regular life. By creating a second tree of life, we might create a second evolutionary arms race, with mirror life on the losing side. Mirror organisms might struggle to find food they need to proliferate. Or not — evolution is a funny thing — but at this point there's no way to know for sure.
"The more I think about this, the more I realize that the real concern ought to be with creating life on this side of the mirror," Perrin told me. Trying to shut down work on creating mirror life "makes no sense. …What would have happened if we put a total moratorium on researching radioactivity? We wouldn't know anything about RNA. And we wouldn't have any radioactive treatments for cancer."
He thinks that red lines can be drawn — when people come closer to actually generating mirror life.
Gigi Gronvall, an immunologist and senior scholar at the Johns Hopkins Center for Health Security, and biosecurity expert at Johns Hopkins University, told Science News that the paper's concerns were very theoretical. While she strongly supports the authors' advocacy for discussion around the issue, she thinks that any proposed funding and research ban "puts the cart before the horse" and could impede research leading to surprising scientific advances.
We don't fully understand the risks of mirror life, and we won't without more research. But this research could be purely computational, allowing us to assess the nature of potential threats without posing real biological risks.
Creating mirror life could help us understand the origins of life and why it evolved in the direction that it did. I'd be lying if I didn't say that the idea of a second tree of life, side B of the biological recording, is really cool. That's not to say that we shouldn't be worried about potential risks here. This is completely new territory, and it might not remain the stuff of science fiction forever. But there is a debate to be had, and more evidence may emerge.
And we really do need these discussions. I'm glad that the Mirror Biology Dialogues Fund is hosting events to facilitate them. It's unusual to have the opportunity to proactively shape biotech governance well before the technology becomes a real possibility. Certainly, there's more to come.
