The final programme documents the Rift Valley's savannah ecosystem. In the rain shadow of the Ruwenzori Mountains, rainfall is sporadic. Acacias are the only trees that can survive the prolonged droughts, but their proliferation is curbed by browsing animals. Giraffes, gerenuks and dik-diks are all specialist acacia eaters, but elephants are the true architects of the landscape. On the plains, grass is the dominant vegetation, sustaining the largest grazing herds on earth. Antelopes use the long grass to conceal their young from lions, cheetahs and other predators. A unique starlight camera enables filming to continue after dark using available light, revealing hitherto unseen behaviour. In the pitch blackness, three lion cubs practise their hunting skills as their mother digs warthog piglets from their burrow. Hippos roam the grasslands by night, but must return to water before sunrise. At the isolated pools of Mzima, stranded hippos starve to death during the prolonged drought of 2009. Those animals that can follow the rains of the Rift Valley on seasonal migrations. Olive baboons are one of the few primates adapted to the savannah, but even they must return to the safety of the trees at night. Despite their well-developed brains, chimpanzees are confined to forested areas such as Kibale in Uganda. The final scenes suggest that the Rift Valley, where our human ancestors stepped out of the forest, is the "cradle of humanity". Inside the Great Rift reveals the challenges of capturing the first starlight footage of sleeping chimps.