BEN NOVAK WAS in a bookstore at the age of 13, thumbing through an oversize volume from the National Audubon Society, when he saw the photograph that changed his life.

The picture was small, but the bird at its center was grand: the blue crown, the bronze neck, the wings cocked just so.

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NATURE, SAYS HANK Greely, is a system utterly enmeshed with humanity and irrevocably changed by it. “In the last 100,000 years, we have altered nature so fundamentally that, if you view nature as what humans haven’t changed — it’s gone,” says the director of the Stanford Center for Law and the Biosciences.

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We are masters of our dominion, for better or worse, and our approach to conservation ought to reflect that, Greely says. We can’t just retreat — just wall off a bunch of nature preserves — and hope the world will re-wild. “We can’t just be stewards or park rangers,” he says. “We’ve got to be gardeners. We have to make choices.”

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But the possibility of revival is already a subject of public conversation. “The worst of all possible worlds is people thinking it can be done when it can’t,” Greely says.