Only the toughest animal species can endure the extreme weather, scarce food and limited oxygen available on the Earth’s highest mountains.

Dive beneath the surface of Earth’s dynamic oceans to uncover the extreme conditions to which animals must constantly adapt.

In the grasslands, animals endure freezes, fires, floods, and droughts. Bull elephants clash in mating battles. Cheetahs and gazelles engage in a predator-and-prey dance in the Kenyan savanna. Bison battle a blizzard while being pursued by wolves.

Jungles comprise the most diverse habitats on Earth in which only the most resilient species triumph. The fiercest jungle species include jaguars, caimans, gibbons, orangutans, spectral tarsiers, hummingbirds, and parasites.

Deserts are getting even hotter, drier and bigger, yet a host of remarkable animals still survive in the harshest of conditions, including cunning hyenas, pint-sized meerkats and sand-dwelling spiders.

The frozen poles are home to the planet's ultimate survivalists, including polar bears, penguins and Arctic wolves. Their world is changing fast -- breaking apart under their feet -- and their resilience will be tested beyond the extreme.