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.
This episode is a pioneering exploration of the latest discoveries concerning the Amazon - by far the greatest river on Earth. It is the river of superlatives, flowing more than 4,000 miles from the Andes to the Atlantic. Its 1,100 tributaries drain the greatest river basin on the planet and along its incredible journey it collects and transports one-fifth of the world's fresh water. Due to its enormous size, it still hides secrets.
Finding somewhere to keep safe is one of the biggest challenges an animal faces. But some animals don't have to find a safe place - they build one. Chris reveals some of the best building animals in the world - a group that is incredibly varied. Accomplished animal architects include everything from beavers to bees and prairie dogs to bowerbirds. They don't only build homes, however - they also make structures to raise their young, store food, catch prey and impress mates. But what can be learnt from their building brilliance?
What is it that makes things alive? What if we made robots that could sustain themselves? What if they could mine metals or recycle old robots, reprogram and remake themselves? There's nothing there we would traditional call alive, but they would have at least have the essence of this perpetual rube Goldberg machine.