Episode one: First Ancestors
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.
Just a few million years previously, Africa was covered, almost edge-to-edge, with dense rain forest. Our ancestors almost certainly used all four limbs to move and live and hunt in their tree-top homes. But massive geological turmoil changed their destiny.
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 film follows a close-knit troop of afarensis, and in particular, Lucy and her young infant. Led by a strong alpha male, there is harmony in their lives. They sleep high in the trees and spend most of the day foraging for food. But then tragedy strikes. While drinking from a nearby river, a lone crocodile sneaks in unnoticed and catches the alpha male unawares.
Now leaderless, a dispute for dominance between the two secondary males unsettles the troupe. Added to that, a rival troupe invades Lucy's territory. While not uncommon in their chimp-like lifestyles, the resultant turf war is both violent and extreme and has devastating consequences.
As the troop's life moves on, 'First Ancestors' shows how although bi-pedalism offers only slight advantages to the afarensis, it opens the door to an astonishing set of new skills and abilities that will change the shape of human life on Earth forever.
Next: The science of episode one