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.