This episode explores the various sea-living invertebrates, form the shores of Morocco to Delaware Bay.

Over 400 million years ago, tiny plants began to invade the land, followed by the first animals - the ancestors of scorpions, millipedes and insects

The role of a few of the millions of insect species, some of which have developed extremely close relationships with plants. Insects pollinate flowers and in some cases neither flower nor insect can survive without the other.

A look at some of the 30,000 species of fish which exist in populations of billions. They can fly, produce electricity, survive in hot soda lakes or under the Antarctic ice. Some, like the salmon, even migrate across oceans and up waterfalls

Some 350 million years ago, evolution reached one of its most crucial stages when fish crawled from water onto the land and became amphibians. Today, newts, salamanders, toads and frogs still survive in great quantities, and there is even one species of frog where the male gives birth from its mouth!

A look at the evolution of mammals from reptiles 200 million years ago. This remarkable transition involved the development of mechanisms for regulating body temperature, for allowing the young to develop in the womb and for suckling newborns. Attenborough also explores the South American origins of marsupials and their colonization of Australia

A look at some of the huge variety of mammals. Bats number over a thousand species, many hunt insects, some sip nectar, drink blood, and even catch fish. Contrast those which use sonar with the great whales that sing, the star-nosed mole and the giant anteater, and the potential variations become dramatically clear

Explore the eternal duel between the hunters and the hunted - one of the driving forces of evolution. As the hunters develop speed and cunning, the prey becomes increasingly fast and wary in order to stay alive. Nowhere is this seen better than on the plains of East Africa