The natural world is full of colours. For us, they are a source of beauty, but for animals they are a tool for survival. David Attenborough reveals the extraordinary ways in which animals use colour: to win a mate, to fight off rivals and to warn enemies. New camera technologies - some developed especially for this series – also allow us to see colours and patterns usually invisible to human eyes.
Ultraviolet cameras reveal bright signals on a butterfly’s wings and facial markings on yellow damselfish that are used as secret communication channels. Some animals can also detect polarized light, and specialist cameras can now show us how fiddler crabs see the world, and how mantis shrimp have strange polarization patterns on their bodies to signal to a mate or rival.

It really is a big bad world out there. So what happens if you are the little guy? This film tells the epic survival stories of the world's smallest animals. To make a living, these tiny heroes have evolved extraordinary skills and achieved mind-boggling feats. From the animal kingdom's greatest artist to the tiny creatures that provide us with so much of the air we breathe, we discover what it takes to be a miniature miracle.

Sagan discusses the story of the Heike crab and artificial selection of crabs resembling samurai warriors, as an opening into a larger discussion of evolution through natural selection (and the pitfalls of intelligent design). Among the topics are the development of life on the Cosmic Calendar and the Cambrian explosion; the function of DNA in growth; genetic replication, repairs, and mutation; the common biochemistry of terrestrial organisms; the creation of the molecules of life in the Miller-Urey experiment; and speculation on alien life (such as life in Jupiter's clouds). In the Cosmos Update ten years later, Sagan remarks on RNA also controlling chemical reactions and reproducing itself and the different roles of comets (potentially carrying organic molecules or causing the Cretaceous–Paleogene extinction event).

David Attenborough reveals the extraordinary ways that some animals use colour to hide and disappear into the background. New science reveals how the Bengal tiger in central India uses its orange-black stripes to hide from its colour-blind prey. In Kenya’s Masai Mara, the zebra’s black-and-white pattern confuses predators with an extraordinary effect called motion dazzle. And on the island of Cuba, a small snail uses colourful stripes in a surprising way to hide from its enemies.
Other animals use colour to trick and to deceive. On Australia’s Great Barrier Reef, a blue-striped blenny uses colours to mimic other fish and launch a sudden attack. In the grasslands of Zambia, the chick of a pin-tailed whydah mimics the patterns of its nest mates to ensure that it is not detected as an imposter. And specialist cameras reveal how a tiny crab spider uses bright ultraviolet colours to lure in its victims.

The tropical Indian Ocean is home to the Spice Islands. Characterised by beautiful sandy beaches, fringing coral reefs and coastal mangrove forests, this is a vibrant nursery area for marine life, such as whale sharks, crabs, seahorses and a great variety of fish. The coastal areas are where humans have the most direct impact on the ocean's resources.

This second episode is a captivating exploration of the ocean's wonders and mysteries. It reveals how a significant part of our planet remains unexplored, primarily due to its vast water coverage. The film emphasizes the extraordinary discoveries awaiting every journey below the water's surface, with over a thousand new species identified annually. Home to 80% of all animal life on Earth, the ocean's diverse habitats host a range of surprising behaviors and life-and-death struggles, often hidden beneath a serene exterior.
The shallow tropical seas, appearing as paradises, are actually arenas of intense survival battles. Predatory lionfish, with their patient hunting tactics, and clown frogfish, using a unique fishing rod-like dorsal fin as a lure, demonstrate the ocean's complex food web. The documentary also explores the kelp forests off the North American coast, revealing their role as nurseries for young horn sharks. Amidst these underwater forests lurk giant sea bass, wolf-eels, and various sharks like houndsharks and broadnose sevengills, posing significant threats to the smaller inhabitants. The episode takes viewers to the twilight and midnight zones of the ocean, unveiling alien-like creatures such as the siphonophore, glass squid, and gulper eel, adapted to the extreme conditions of deep waters. The journey concludes with the moving story of the pearl octopus, whose devotion to her eggs in the challenging deep-sea environment is both heartwarming and heartbreaking.
This episode is not only a showcase of the ocean's diverse inhabitants but also a reminder of the urgent need to understand and protect this vast, mysterious, and vital part of our planet.