Homo ergaster is an extinct chronospecies of Homo that lived in eastern and southern Africa during the early Pleistocene, about 1.9 years ago. There is still disagreement on the subject of the classification, ancestry, and progeny of H. ergaster, but it is now widely accepted to be the direct ancestor of later hominids such as Homo heidelbergensis, Homo sapiens, and Homo neanderthalensis rather than Asian Homo erectus. It is one of the earliest members of the genus Homo, possibly descended from, or sharing a common ancestor with, Homo habilis.
Homo ergaster is believed to have diverged from the lineage of H. habilis between 1.9 and 1.8 million years ago; the lineage that emigrated Africa and fathered Homo erectus diverged from the lineage of H. ergaster almost immediately after this. These early descendants of Homo ergaster may have been discovered in Dmanisi, Georgia. Homo ergaster remained stable for around 500,000 years in Africa before disappearing from the fossil record around 1.4 million years ago. No identifiable cause has been attributed to this disappearance; the later evolution of the similar Homo heidelbergensis in Africa may indicate that this is simply a hole in the record, or that some intermediate species has not yet been discovered.
Homo ergaster used more diverse and sophisticated stone tools than its predecessor, Homo habilis, developing the first Acheulean bifacial axes. The use of Acheulean tools began approximately 1.6 million years ago, the line of Homo erectus diverged some 200,000 years before the general innovation of Acheulean technology. Thus the Asian migratory descendants of Homo ergaster made no use of any Acheulean technology. Sexual dimorphism in Homo ergaster is greatly reduced from its australopithecine ancestors, but still greater than dimorphism in modern humans. This diminished competition for mates between males. Not only was Homo ergaster like modern humans in body, but also more in organisation and sociality than any earlier species. It is conceivable that Homo ergaster was the first hominin to harness fire: whether as the containment of natural fire, or as the lighting of artificial fire, is still a matter of contention.