Researchers are working to revive the passenger pigeon, once the most abundant bird in the world, and the woolly mammoth, which they say could slow down the melting of Arctic permafrost. It may be possible, but is it right to turn back the clock?
As conservation scientists struggle to stem the catastrophic loss of biodiversity, some synthetic biologists are working to bring extinct species back to life. Some believe it's the right thing to do to atone for driving species extinct. But many conservation biologists say it's far more important to save those still among us.