David Attenborough examines more fascinating creatures. Here David looks at some of nature's most extreme babies, including giant pandas and kiwis.

David Attenborough investigates two shells that have proved to be winners in evolution: the bird's shell and the hard shell of the tortoise. The ostrich egg is so strong it's possible for a person to stand on it without it breaking – 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.