Extinction is deeper than death—it’s an irreversible biological loss that extends well beyond individuals. At least, that’s what we’ve always understood it to be. Now, some researchers are betting that, in certain cases, extinction might be able to be undone. The emerging field of de-extinction seeks to revive lost species using advances in synthetic biology, including cloning. While resurrected individuals would not be exact genetic replicas of their ancestors, scientists believe that they can create very close proxies—so close that the animals would fill a niche left vacant by the species’ disappearance. “The only thing we’re interested in is conservation benefit, which we’ve defined in terms of restoring some missing ecological function,” says Philip Seddon, a zoologist at the University of Otago in New Zealand who is involved with drafting de-extinction guidelines for the International Union for Conservation of Nature. Environments aren't static...