The first episode tells how invertebrates became the first creatures of any kind to colonise dry land. Their forerunners were shelled and segmented sea creatures that existed 400 million years ago. Some of them ventured out of the water to lay their eggs in safety, and Attenborough compares those first steps with today's mass spawning of horseshoe crabs off the Atlantic coast of North America.
2005 • Nature
The next programme deals with flying insects. It begins in Central Europe, where the Körös River plays host to millions of giant mayflies as they rise from their larval skins to mate. — the climax of their lives. Mayflies and dragonflies were among the first to take to the air about 320 million years ago, and fossils reveal that some were similar in size to a seagull. Damselflies are also looked at in detail.
2005 • Nature
The final programme looks at the superorganisms formed by bees, ants and termites. Attenborough reveals that their colonies, whose individuals were once considered purely servile, are "full of conflict, power struggles and mutinies." They evolved when such creatures moved away from a solitary existence and started building nests side-by-side, which led to a collective approach to caring for their young.
2005 • Nature
A polar bear mother keeps watch over her cub as they wait for the coming winter and the plentiful feeding opportunities it brings. But there are threats abound: from cannibalistic male bears, to the devastating impact of climate change, which has delayed the seasonal freeze and put them at risk of starvation.
Ascends a kapok in the South American tropical rainforest to observe "the greatest proliferation of life that you can find anywhere on the surface of the Earth. There are two main causes for this: warmth and wetness. As this climate is constant, there are no seasons, so trees vary greatly in their flowering cycles.
Patrick follows the grizzly bears that are taking a risk with the weather by leaving their winter dens early. Hungry wolves are struggling to bring down their elk prey in the unusually shallow snow. And for great grey owls, it is the iciness of the snow that is hampering their hunts. Yellowstone's winter is always one of the most brutal on the planet. But 2016 saw weather records broken, and the wildlife was forced to adapt to survive. Kate Humble gets to grips with the science behind this remarkable season, from understanding the importance of the snowpack's structure as the melt begins to uncovering why Yellowstone's unique geology poses problems for some grazer's teeth.
As temperatures hit minus 60 food becomes scarce, and animals such as foxes and hares shed their colourful coats to camouflage themselves in the snow. The end of winter heralds one of the world's greatest feeding frenzies as large ocean predators target the millions of fish who have found refuge in the Gulf of Alaska.