Extinction is supposed to be permanent, an irreversible door slamming shut. But the Pyrenean ibex, or bucardo, holds a unique and tragic record: it is the only species known to have gone extinct not once, but twice. This episode tears up the textbook definition of extinction to explore de-extinction, the hard limits of cloning technology, and the messy reality of trying to play Mother Nature.

We profile this rugged Iberian mountain goat, its seasonal adaptations and dramatic sexual dimorphism, then trace its collapse from 50,000 individuals to a single animal named Celia, killed by a falling tree in 2000. A year earlier, scientists had cryopreserved her ear tissue, setting up an unprecedented cloning effort using somatic cell nuclear transfer that produced a clone in 2003, only for it to die within minutes from a fatal lung defect.

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