The Africa of two million years ago is a crossroads in human evolution. Half a dozen or more different species of ape-men exist alongside one another. Each of them has exploited the environment in a different way and has developed their own strategy for survival.

'Blood Brothers' follows the lives of two species, Paranthropus boisei and Homo habilis who embody two alternative ways of ape-man life. Although heavyset, with distinctive gorilla-like faces, the boisei are gentle characters. They live within a strict social structure and are led by a dominant male whose strength and power holds the group together.

They are adapted brilliantly to the tough conditions in this dry arid land. Their huge teeth, four times the size of our own, and strong jaws mean they can eat the toughest vegetation. For them dried tubers and reed roots are rich pickings.

The habilis have taken a different approach to survival. They don't have the specialisms of the boisei but instead have developed into the archetypal jack-of-all-trades, inquisitive scavengers prepared to try almost anything to survive. Tough, active, gregarious and noisy, they are always on the move and always alert to the possibility of a meal. But in the near drought of the dry season the habilis are struggling. It seems as if their way of life cannot help them when conditions are tough.

However habilis have a secret weapon. They have come to use brainpower rather than brawn. They've learnt to work together to scare other predators away from food. They scavenge for meat and, perhaps most importantly, make basic stone tools - equipping themselves through their own efforts with the kind of specialist eating equipment creatures like the boisei have by nature.

But which strategy for survival will win out? Which of these ways of living is still present in us? As is often the case in our story, nature has a say: Massive geological turmoil means the habilis and boisei environments continue to change. The boisei's specialisms have locked them into one way of living, and when their niche no longer exists, neither can they. But the habilis can adapt to a changing world - their generalist trait lives on in us.