Exemplar: KNM-ER 3733 [Koobi Fora] - 1.7 million y.a.There is near unanimity among paleoanthropologists that HOMO ERGASTER, which appeared about 2 million years ago, is the anchor species for all subsequent humans.
Ergaster presents a significant increase over earlier hominids in both stature and bone mass. Male ergasters stood close to 1.6 meters tall and weighed around 65 kilos, making them physically almost the equal of modern Africans. With that robust evolutionary shift, brain capacity increased to 850cc and the skull aquired a definite browridge and an elongated "football" shape (most likely the result of expanded frontal and occipital lobes).
Long legs and increased brain size made ergaster especially suited to long-range migration. The available fossil record suggests that ergaster ranged throughout eastern and northern Africa, and was the first human species to migrate out of Africa into middle and eastern Asia -- possibly even into southern Europe.
Ergaster is also associated with the rise of the Acheulean tool industry around 1.4 million years ago. These are elegant implements, chipped with great care to functionally specific tool shapes, but also much more massive than the tools used by previous hominids (in some cases, nearly too massive for these earlier hominids to carry). This diversity of tools, in designs that remain unchanged across hundreds of thousands of years, implies specialization in hunting and in the processing of animal and plant products.
In ergaster appears many of the social and behavioral traits characteristic of human hunter-gatherer populations of today -- knowing resource exploitation of very large geographical areas, long term stability in toolmaking procedures, complex plant and animal processing skills -- which all imply early forms of vocal or gestural language and a considerable role for culture and social learning.