It's 3.5 million years ago and in East Africa a remarkable species of ape roams the land. Australopithecus afarensis has taken the first tentative steps towards humanity by standing and walking on two legs. The rift valley was forming, and the rain forests dying as Africa dried out - turning the landscape into a mosaic of scattered trees and grass. In this new environment afarensis found it more efficient to move about on two legs rather than four.

This edition explores the vast grasslands of the continent, hauntingly beautiful regions inhabited by strange creatures - giant anteaters, armadillos, maned wolves, capybara and jaguars.

Roses are red, violets are blue but according to the latest understanding these colours are really an illusion. One that you create yourself. Horizon reveals a surprising truth about how we all see the world. You may think a rose is red, the sky is blue and the grass is green, but it now seems that the colours you see may not always be the same as the colours I see. Your age, sex and even mood can affect how you experience colours. Scientists have unlocked the hidden power that colours can have over your life - how red can make you a winner, how blue makes time speed up. Watch an experiment where for people in a blue pod, a minute lasts 11 seconds shorter.

There are 200 million insects for each of us. They are the most successful animal group ever. Their key is an armoured covering that takes on almost any shape. Darwin's stag beetle fights in the tree tops with huge curved jaws. The camera flies with millions of monarch butterflies which migrate 2000 miles, navigating by the sun. Super slow motion shows a bombardier beetle firing boiling liquid at enemies through a rotating nozzle. A honey bee army stings a raiding bear into submission. Grass cutter ants march like a Roman army, harvesting grass they cannot actually eat. They cultivate a fungus that breaks the grass down for them. Their giant colony is the closest thing in nature to the complexity of a human city.

Grasslands feed the world. Over thousands of years, we humans have learned to grow grains on the grasslands and domesticate the creatures that live there. Our success has propelled our population to almost seven billion people. But this episode reveals that, even today, life in the 'Garden of Eden' isn't always rosy. We walk with the Dorobo people of Kenya as they bravely attempt to scare off a pride of hungry lions from their freshly caught kill. We gallop across the Steppe with extraordinary Mongolian horsemen who were 'born in the saddle'. And in a perfect partnership with nature built up over generations Maasai children must literally talk to the birds! The honeyguide leads them to find sweet treats, but they'll have to repay the favour.

The tale of one of China's most famous dynasties begins with the amazing story of Hongwu, a peasant rebel who founded one of greatest eras in Chinese history. The film takes us to his great capital Nanjing, with its 21 miles of walls, each brick stamped with the name of the village that made it. Following the trail, we go to the Bao family village and see the villagers act a Ming murder story.
Like many authoritarian states, the Ming were obsessive about architecture. We see the giant fortifications of the Great Wall, the ritual enclaves of the Forbidden City in Beijing and travel with bargeman Mr Hu down the Grand Canal, China's great artery of commerce right up to the present day. We then hear about Admiral Zheng He's voyages to Africa and the Gulf decades before Columbus, watch the construction of an ocean-going wooden boat 250ft long, and hitch a ride on a replica Ming junk in the South China Sea.
As state prosperity grew, so did a rising middle class. Wood looks at Ming culture in Suzhou, the 'Venice of China'. Staying in a merchant's house, he discovers the silk, ceramic and lacquer-making industries, and visits one of the most beautiful gardens in the city. Then on to Macao and the arrival of Jesuit missionary Matteo Ricci, who hoped to convert China to Christianity. In the cathedral in Beijing, we learn more about these fateful exchanges with the west. Finally in Shaoxing, we visit the house of the 'Ming Proust' and at grassroots the Zhao family in Fujian where the film ends in an elegiac mood with the fall of the Ming in 1644.