One of the most famous finds at Lake Turkana, Northern Kenya, is the cranium of an early species of Homo, known as Australopithecus boisei. However, in the same sedimentary layer, another cranium was also found belonging to a species of hominid named Homo ergaster. This hominid species is believed to be a different geographical population of Homo erectus.

Many aspects of Homo ergaster and Homo erectus anatomy are, of course, similar, with the principal differences being a higher cranial vault, thinner cranial bone, absence of sagittal keel, and certain cranial base characteristics in Homo ergaster. One distinguishing feature between early Homo and ergaster/erectus involves increased brain size (ranging between 850 and 1100 cm³, with an increase over time), although the increase in body size actually means that the relative brain size has increased but little.

Other distinguishing features include a long, low cranium (particularly in Homo erectus), the presence of brow ridges, a shortened face, and a projecting nasal aperture, suggesting the first appearance of the typical human external nose with the nostrils facing downward. The structure of the nose would permit the condensation of moisture from exhaled air, which would have proved beneficial in a species that pursued an active subsistence strategy in warm, arid habitats, such as those occupied by early Homo ergaster.

Early Homo gave rise to a large-bodied, large-brained speices in Africa approximately 2 million years ago, but this species is now called Homo ergaster by many anthropologists. Homo ergaster expanded its range beyond Africa and into Asia soon after its origin and at least by 1.8 million years ago; it then gave rise to Homo erectus in those areas. Homo erectus expanded its range throughout Asia, back into Africa, and presumably into Europe. Approximately 150,000 years ago, a speciation event in Africa gave rise to Homo sapiens (probably from Homo ergaster, but possibly from Homo erectus), which then spread into the rest of the Old World, and subsequently into Australia and the Americas.

Height	1.3 – 1.7 metres
Physique	Robust, but "human" skeleton
Cranial Volume	750 – 1250 cm³
Known Date	1.8 – 1.2 million years ago
Distribution	Africa into Asia
Skull form	Higher cranial vault, thinner cranial bone, absence of sagittal keel and certain cranial base characteristics
Jaws/Teeth	Robust jaw in larger individuals; smaller teeth than H. habilis