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The creation of a “mirrored” organism could “trigger severe ecological disruptions,” according to a 300-page technical report released today. Its authors claim such organisms could quickly spread across the world, fatally infect humans, and “directly drive vulnerable plant and animal species to extinction.” The report accompanies an article in Science, also released today, entitled “Confronting Risks of Mirror Life.” But what, exactly, is a mirrored organism? To answer that, let’s consider how extant life works. Proteins, sugars, lipids, and nucleic acids — key molecules used by cellular life — are all “chiral,” a term derived from the Greek for “hand.” Just as our hands cannot be perfectly aligned on top of one another regardless of how they are rotated, despite being mirror images, the same is true of chiral molecules. The two mirror images of a chiral molecule are called its enantiomers; they possess the same atoms connected in the same order, but with mirrored three-dimensional arrangements. One enantiomer of a molecule might fit perfectly into a protein receptor, while the other may not fit at all. This is no mere quirk of biology, but a crucial and ubiquitous feature of it. A mirrored organism would use right-handed molecules everywhere a naturally-occurring organism uses left-handed ones, and vice versa. It could thus elude the typical chiral interactions by which microorganisms hunt their prey. A mirrored bacterium would be totally resistant to bacteria-infecting viruses, called bacteriophages (or just “phages”). It would also be undetectable by key parts of the human immune system. Such mirrored invaders could theoretically spread across the Earth while evading the biological defenses that have evolved to check such threats. Experts say that mirrored organisms are still decades away from being a reality. But out of caution, the new report signals alarm well in advance. For the article in Science, more than 30 scientists from ten countries are calling