David Attenborough asks three key questions: how and why did Darwin come up with his theory of evolution? Why do we think he was right? And why is it more important now than ever before?
Footage of wildlife inhabiting underwater kelp forests, including thousands of giant cuttlefish spawning along a restricted area of rocky reef off the south coast of Australia. Males outnumber females 11 to one, which leads to fierce competition. Larger males use brute force to drive off competition, while their smaller rivals use deception by mimicking the appearance of females. The programme also features tiger sharks hunting for green turtles in fields of seagrass and spider crabs trying to avoid predators while they shed their shells.