Homo ergaster (meaning "Workman") were African hominids that lived between 1.9 and 0.6 milion of years ago. They are the direct descendants of Homo erectus and they were the first creatures to master the art of tracking. Their greater intelligence is due to the large quantities of meat, essential to their big brains (that had 74% of the size capacity of a modern human brain). The Males were around 1.8 metres tall and the females were around 1.6 metres tall. They had more hunting techniques than any other hominid before them, such as kill their preys by exhaustion. They also used stone tools called bifaces, two-sided tools.