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Mirror life could end all life on Earth. That sounds dramatic, but senior biologists have raised the alarm about experiments happening all around the world. It sounds like something in a Doctor Who plot, but no – mirror life is a real possibility. So why do scientists want to create something that’s potentially apocalyptic? Well, it could also have huge benefits (think back to splitting the atom). The first thing to say, however, is that mirror organisms are still a little way away yet – but only decades, not centuries. So far, scientists have only made mirror molecules, one of life’s building blocks. What for? Life works because its building blocks fit together. Imagine drilling a screw into a piece of wood. The screw cuts a hole with a thread that snugly matches its own. If, for some reason, the Doctor showed up and handed you a mirror version of the screw, its thread would be in reverse. It wouldn’t twist into the hole you’d just made as the threads wouldn’t match. That said, the mirror screw would still work; you’d just have to create a mirror hole for it. Mirror molecules, including DNA, work a bit like that. They follow the same principles as the biology around us, but they’re entirely incompatible with traditional biological functions. In medical terms, this means they’re effectively invisible to your body’s systems. Our biology doesn’t have the tools to recognise these molecules and break them apart. And if someone took these mirror molecules and put them together to make a cell and then an organism… you’d have mirror life. But we don't have any way of breaking it down. If it escaped the lab, we’d just have to hope it didn’t have an appetite.

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