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Well, The Doctor Has Two Hearts


The titular Doctor of the British sci-fi show Doctor Who is a time-traveling alien who sure looks human, but has and has seen some remarkable biology.

Robert Kruger at Cell writes that the Doctor, when close to death, can regenerate into a new form (or as a new actor takes the reigns of the show), but even on Earth, a number of organisms can re-grow tissue, though perhaps not quite as dramatically. For example, Kruger says that researchers were able to remove lens tissues from some newts' eyes 18 times and watch new tissue grow back, new tissue that seemed no different than the earlier lenses.

A number of episodes themselves, Kruger adds, play on biological themes. In one that Kruger focuses on, the Doctor confronts a species called the Adipose whose oddly cute offspring were formed through parthenogenesis in people taking certain diet pills. Kruger notes that it appears theoretically possible to transform tissue into fat as many regulators of fat differentiation are known, though he adds that changing the chromatin state may also be necessary. "As for how the adipose-based aliens become sentient and mobile, we'll leave that speculation for Doctor Who's 100th anniversary," he adds.