Flamingos of Altiplano, Chile Flamingos of Altiplano, Chile

A lone, hungry wolf hasn't eaten in days. He's traveled hundreds of miles in search of food. Desperate, he finally spies a herd of caribou. They can run faster — but he's got stamina. Who do you root for? Welcome to Untamed Americas, National Geographic's spectacular four-hour docuseries about life on the razor's edge across mountains, coasts, deserts and forests in North and South America. (The first two hours air Sunday at 9/8c, with the final two premiering Monday, 9/8c.) It's an emotional roller coaster about wildlife in its natural element — truly survival of the fittest in a hemisphere of extremes.

"I want to make people aware of it, to care about it and experience it for themselves," says producer Karen Bass. "Let's not kid ourselves that we understand our planet, because we don't. It's inspiration. It's revelation."

As you'd expect from National Geographic, the cinematography is breathtaking — underwater, in snowdrifts, in dust storms — but it's the engaging storytelling that will pull at your heart. Narrated by Josh Brolin, each segment follows an incredible range of animals in their daily life-and-death struggles, which often unfold in surprising ways. Take the grasshopper mouse, who seems sweet — but when a scorpion comes along, "she just goes for it," says Bass. "She proves fearless when it comes to defending her babies." Cracks Brolin in the voiceover, "She's a wolf in mouse's clothing."

And then there are the penguins of the Atacama desert in southern Peru. "Faced with the edge of the cliff," says Bass, "they go sandboarding right down the edge. Talk about character!"

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