Editor's note: When allowed to regulate naturally, populations will stabilize — in other words, the wolves won't eat all the elk, etc. Wolf numbers have risen and fallen with the availability of prey, along with disease and other factors.

Not quite 20 years ago the experiment to recover wolves in Yellowstone National Park got under way with a relative handful of Canadian wolves brought into the park. Today that genetic feedstock has produced what biologists had hoped for: a more natural wild kingdom, one with checks and balances on itself.

"In 2003, we had 174 wolves, now we have 88. Our policy is to preseve and protect, so what we’re shooting for is what I’d called a natural density," says Doug Smith, a wildlife biologist who oversees the park's Wolf Project. “We’re at that now."

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