Through the influence of Ernst Mayr [4], the category Homo erectus became a catchall for a large and unwieldy assortment of fossils of substantially differing morphologies over a vast time span [5]. It was in 1975, that Groves and Mazak [6] addressed this by declaring KNM-ER 992 as the holotype of a new species Homo ergaster. Homo ergaster means ‘work man’ or ‘working man’, it was given this name because large stone tools were found near some of its fossils [7].  KNM-ER 992, a mandible found in Ileret, Kenya, was initially allocated as Homo sp. [8]. Initially, this innovation was dismissed by the Koobi Fora team and other influential workers [9], but eventually, many authors have begun to use this new name in place of “African Homo erectus” especially for Homo of the 2- to 1- year period [5].

Those that support Homo ergaster being incorporated into Homo erectus, believe that there is too little distinction between the two to classify them as distinct species. While those who support keeping the two species distinct point to the significant morphological differences between the African and Asian fossils [1].

Homo ergaster is characterized by a pattern of features more resembling modern humans than the earlier contemporaneous australopithecines and paranthropines. These features include larger relative brain sizes, larger body mass, slower rates of growth and maturation, relatively long legs, dedicated bipedal locomotion, and smaller teeth and jaws. It differs from earlier possible members of the genus Homo such as Homo habilis and Homo rudolfensis by having more complex skeletal and dental features, indicating a lifestyle that was more similar to that of modern humans [10][1]. 

Many characteristics of Homo ergaster are shared with Homo erectus, such as large forward-projecting jaws, large brow ridges, and a receding forehead [11][1]. Many of Homo ergaster's features are clearly more primitive versions of later expressed features in Homo erectus, which obscures the differences between the two [12][1]. East African and East Asian fossils differ in subtle but potentially significant ways. Among these are Homo ergaster’s slightly higher-domed and thinner-walled skulls as well as the even more massive brow ridges and faces of Asian Homo erectus [11][1].

The Homo ergaster is significantly taller than its ancestors. Whereas Lucy, a famous Australopithecus fossil, would only have been about 1 m (3ft 3in) tall at her death, Turkana Boy was about 1.62 m (5ft 4in) tall when he died and would probably have reached 1.82 m (6ft) or more if he had survived to adulthood [11]. Adult Homo ergasters are thought to have ranged in height from about 1.45 to 1.85 m (4ft 9in to 6ft 1in) tall [13][1].

Diet 

The larger body size in Homo implies a corresponding increase in either the daily amount of food eaten or the quality of the food in order to meet the increased energy needs. If Homo ergaster ate the same type of diet as the smaller-bodied australopithecines, then they would have to feed more in order to acquire the extra calories required by their larger body mass. Homo ergaster jaws and teeth are smaller, which suggests a major dietary shift away from more fibrous and more difficult to masticate foods [14][15]. Similarly, the Homo ergaster's trunk proportions indicate a relatively small gut, which is compatible with higher quality and a more easily digested diet [16]. The more open xeric habitat occupied by Homo ergaster would also provide different dietary options [10].

Meat was most likely a larger part of the Homo ergaster diet than it was for earlier and contemporaneous australopithecines and paranthropines [16]. However, meat alone is unlikely to have met its increased energy requirements [10]. 

Technology

Homo ergaster inherited the Oldowan culture from australopithecines and earlier Homo [1]. But they soon learned to strike much larger stone flakes, and by 1.65 mya they had created the hand axes and other more extensively flaked artefacts known as the Acheulean culture. They initiated a tradition in which core forms were often deliberately and meticulously shaped [11]. 

Dates 

Argon dating by McDougall et al. [17] provides ages of 1.47±0.03 Ma and 1.44±0.3 Ma for the specimens from the Nachukui Formation in West Tukana, an age range of 1.65±0.05 Ma to 1.43±0.04 Ma for the material from the Karari Ridge at Koobi Fora, and an age of 1.50±0.04 Ma for the remains from Ileret region of Koobi For. With this, the conservative age of Homo ergaster according to Wood & Boyle [18] is 1.74 to 1.4 Ma. 

Specimens from Swartkrans Formation attributed to Homo ergaster are Members 1,2, and potentially Member 3 (postcranial remains). These specimens yielded an estimated age range of 2.19±0.08 to 0.96±0.09 Ma  [19]. These specimens are not universally accepted as belonging to Homo ergaster, but these dates will push the range to 2.27 to 0.87 Ma Wood & Boyle [18].