Homo ergaster (1.9–1.4 MYA), was as tall as modern humans, with a similar build, and much the same feet. Brain size was 600–910 cm2. H. ergaster lived in east and south Africa.
The classification, ancestry, and progeny of H. ergaster remains controversial. H. ergaster is widely considered the direct ancestor to later hominins: H. heidelbergensis, H. neanderthalensis, and H. sapiens. H. habilis is the putative ancestor of H. ergaster. Whether H. ergaster and H. erectus are separate species is still debated. They had slightly different skull bone structures near the eyes (supraorbital foramen) and H. ergaster had a thinner skull.
With a vertical posture built for long distance travel, H. ergaster became less hairy and evolved better sweat glands, improving endothermy. Panting respiration was replaced by controlled breathing, opening the way for more robust sound production. H. ergaster appears to be the first hominin with humanlike vocal cords. Altogether, the scenario seems of more communication at some distance rather than just at close quarters.
H. ergaster was an innovative stone tool maker, developing the bifacial ax 1.76 MYA. Such axes were used for cleaving a variety of materials, including animal hides and vegetative matter. Some were doubtlessly employed as weapons. Given the large volume of finds in the archeological record, these skills appear culturally transmitted.
Compared to australopiths, sexual dimorphism was reduced by about 20% in Homo generally. The sex size difference in H. ergaster exceeded that of modern humans.