The evolution of the vertebrates, animals with backbones, is one of the greatest stories in natural history. From crocodiles and whales to tigers, birds and humans, their kind is extraordinary for their beauty, variety and adaptability. For millennia, they have developed astonishing ways of living in all the world's environments. David Attenborough, who has a unique perspective on them all, embarks on a remarkable journey of discovery. Now new scientific discoveries and living fossils, animals with biological links to their ancestral past, enable him to tell the fascinating story of how animals have come to be the way they are today.