David Attenborough investigates two shells that have proved to be winners in evolution: the tortoise's shell and the shells of birds' eggs. The ostrich egg is so strong it is possible for a person to stand on it without it breaking, but how does the chick break out of this fortress? The evolution of the tortoise shell was for a long time a mystery and this bony box offers a lot more than just protection.
The Rockies are the spine of North America, a beautiful wilderness of snow-capped peaks and hidden valleys. Cougars hunt in abandoned ranches, wolverines search the deep snow for food and grizzly bears hunt in the high mountain meadows. Daredevil wingsuit flier’s leap from mile-high cliffs and Native American tribes compete in breakneck horse races. It is also the range of surprises, with tiny cannibal salamanders hunting in mountain ponds and hummingbirds making enormous migrations
Steve Backshall leads a team of elite explorers - including world leading underwater cave explorer Robbie Schmittner, former Royal Marine Aldo Kane and diving camera operator Katy Fraser - into the wilds of the Yucatan Peninsula in Mexico. Under the vast jungle here is the largest unexplored network of caves in the world, comprising thousands of kilometres of passageways. They are stunningly beautiful but incredibly dangerous - much of the system is under water. First the team must trek through tough, scorpion-infested jungle to camp alongside a giant sinkhole in the jungle floor - a dark gateway to an underworld full of nightmarish creatures.