Predators and prey must evolve speed, endurance and manoeuvrability to outwit each other, and the pack hunters must maintain order in the ranks.

With perfect streamlined bodies and great underwater speed, seals, dolphins, porpoises and whales became the new hunters of the sea..

The natural world was transformed when one great ape began to walk upright - us. But why has this led to the development of our extraordinary brains?