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 next instalment describes the move from water to land. The fish that did so may have been forced to because of drought, or chose to in search of food. Either way, they eventually evolved into amphibians. Such creatures needed two things: limbs for mobility and lungs to breathe. The coelacanth is shown as a fish with bony fins that could have developed into legs, and the lungfish is able to absorb gaseous oxygen. However, evidence of an animal that possessed both is presented in the 450 million-year-old fossilised remains of a fish called a eusthenopteron. Three groups of amphibians are explored.
Across the world we are seeing the emergence of bacteria that have gone rogue. These are the superbugs, dangerous bacteria that are becoming resistant to our only defence: antibiotics. Horizon meets the scientists who are tracking the spread of these potential killers around the globe, and discovers the new techniques researchers are developing to help defeat these superbugs.
Two male ocelots, among the rarest wild cats of the Pantanal, are fighting it out over a freshly killed anaconda. In the distance, the loudest land animal in the Western Hemisphere, the howler monkey, fills the air with its primal cry. There's excitement at every turn in this protected South American wetland.
Monterey Bay on California's coast is one of the most diverse marine ecosystems in the world, its giant kelp forest bursting with life, from microscopic plankton to visiting ocean giants. The secret key to success in such a busy microworld is balance. Steve Backshall guides us through the unique geography of the bay and introduces some of its key characters in a quest to find the one species that keeps life in the kelp forest in check.