Episode 2 traces our hair, skin, teeth, jaws and sense of hearing back to reptilian ancestors - from ferocious beasts that ruled the Earth, to a little shrew-like animal that lived 195 million years ago.

In the opening episode, Neil journeys from an American highway to the Arctic Circle to connect our lungs, arms, legs and hands to a prehistoric fish that crawled onto land 375 million years ago.

In the final episode, Neil tracks our hands, feet, colour vision, spine and upright gait to our primate and hominid progenitors, who also passed on perhaps the most important legacy of all - a path to the human brain.