A close-up view of sex, bug-style, as David Attenborough talks viewers through the different ways in which creepy-crawlies reproduce. Size matters for the minuscule male orb spider, creepily sneaking up on its intended and trying to mate without her noticing, while there's no rest for the lothario-like butterfly, which has plenty of notches on its proverbial bedpost. However, the harvestman spider has no use for sex at all, and reproduces by cloning itself.
This episode details the origins of the vertebrates, which lie in the primitive fish that once swam in ancient seas. Remarkable advances allowed them to make the radical move onto land, and then take to the skies with the advent of flight. Brand new discoveries of fossils - ancient and living - combined with stunning CGI enable David to chart their unexpected journey out of the water to populate all corners of the globe.
Plants amazingly dominate this green world by employing poisons, recruiting defensive armies, feeding off the dead and using animals for pollination and seed dispersal. For predators this world presents exceptional challenges, not only in finding prey in such a tangled place, but in how to deal with the toxins that so many animals and plants are laced with.
Grasslands cover one quarter of all land and support the vast gatherings of wildlife, but to survive here animals must endure the most hostile seasonal changes on the planet. From Asia's bizarre-looking Saiga antelope to the giant anteaters of Brazil, grassland animals have adapted in extraordinary ways to cope with these extremes. In the flooded Okavango, lions take on formidable buffalo in epic battles, on the savannah bee-eaters take advantage of elephants to help catch insects and, on the freezing northern tundra, caribou embark on great migrations shadowed by hungry Arctic wolves.