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.
Biologists teach that all living things on Earth are related. Is there any solid evidence to back this claim? Join us as we explore the facts! We start with a close look at the origin of whales from land mammals, and then touch on the origins of several other critters, including our own species.