Persuading the Body to Regenerate Its Limbs

Matthew Hutson in The New Yorker:

Each year, researchers from around the world gather at Neural Information Processing Systems, an artificial-intelligence conference, to discuss automated translation software, self-driving cars, and abstract mathematical questions. It was odd, therefore, when Michael Levin, a developmental biologist at Tufts University, gave a presentation at the 2018 conference, which was held in Montreal. Fifty-one, with light-green eyes and a dark beard that lend him a mischievous air, Levin studies how bodies grow, heal, and, in some cases, regenerate. He waited onstage while one of Facebook’s A.I. researchers introduced him, to a packed exhibition hall, as a specialist in “computation in the medium of living systems.”

Levin began his talk, and a drawing of a worm appeared on the screen behind him. Some of the most important discoveries of his career hinge on the planarian—a type of flatworm about two centimetres long that, under a microscope, resembles a cartoon of a cross-eyed phallus. Levin is interested in the planarian because, if you cut off its head, it grows a new one; simultaneously, its severed head grows a new tail. Researchers have discovered that no matter how many pieces you cut a planarian into—the record is two hundred and seventy-nine—you will get as many new worms. Somehow, each part knows what’s missing and builds it anew. What Levin showed his audience was something even more striking: a video of a two-headed planarian. He had cut off the worm’s tail, then persuaded the organism to grow a second head in its place. No matter how many times the extra head was cut off, it grew back.

More here.