Discuss the main evidence for the earliest dispersal of Homo outside Africa, drawing on the key fossil and archaeological evidence. Discuss the strengths and weaknesses of the prevailing evidence for the early dispersals, and discuss what factors may be involved in limiting the geographic expansion of early hominins.
The prevailing evidence for the earliest dispersal of Homo outside Africa indicates that the first dispersals were carried out by Homo ergaster between 1.8 and 1.0mya; this evidence comprises of direct fossil remains (particularly at the site of Dmanisi and sites in south Asia), and of the more abundant lithic record, using which the movement of Homo ergaster can be traced upwards through Africa, across the Levant and into Asia. Despite some weaknesses in the fossil record in Java, and the lithic record at ‘Ubeidiya, it can be affirmed that migrations began with the emergence of the earliest Homo ergaster species (around 1.8mya), that dispersal was not a specific event but rather constituted a palimpsest of intermittent events (seen through the gradual evolution of industrial style from Oldowan to Acheulean) (Dennell 2003), and that each migration was not one swift movement, but was rather the product of a gradual expansion of the home ranges of various groups. Finally, it can be seen that these Homo ergaster colonisers may have lacked the adaptability of their later H. ergaster counterparts (which emerged in the Middle Pleistocene); rather the limiting factors of habitat type, food abundance and predation, and latitude meant that the earliest migrations were in fact lateral dispersals across one reasonably homogenous habitat type.
One way of establishing when the first hominin species left Africa is directly through the fossil record; the dating of specific fossils, and their assignment to a species, can give us information about the dissemination of Homo ergaster populations into Eurasia, and the subsequent species diversification. Arguably the most significant fossil evidence for the earliest expansion of Homo ergaster beyond Africa has been discovered at the site of Dmanisi, Georgia. The Dmanisi site is located about 85 km southwest of Tbilisi, the capital city of the Republic of Georgia (Gabunia 2001). Excavations of the site have yielded four hominin fossils: in 1991, archaeologists discovered a hominin lower jaw; in 1999 nearly two complete crania were found; and later in the same year a well-preserved cranium and associated mandible was excavated (Robert Boyd 2009). The Dmansi fossils were described as possessing a mix of primitive and derived features. The hominins to which they belonged had relatively small brains (600-775cc), with calculations based on the relationship between brain and body size indicating that the Dmansi hominins fell at the lower end of the size distribution for H. ergaster, and appear more like H. habilis (or Australopiths). They also retained primitive features in certain areas of their shoulder morphology; shoulder and elbow joints do not show the rotation seen in humans, meaning that the palms of the hominins would be naturally orientated towards the front of the body (as opposed to facing inwards). However, derived traits can be identified; Dmansi hominins had the same limb proportions as modern humans, and their lower limbs and feet were well suited to long distance running (adaptation that australopithecines lacked) (Robert Boyd 2009). The oldest strata in which the fossils were found have been dated to 1.8mya, and the primitive features seen on the hominin fossils indicate that these hominins would have been among the first to migrate out of Africa as only fossils assigned to the species H. ergaster and derived hominin species have been identified beyond Africa, and the fact that H. ergaster only emerged between 2.0-1.5mya in Africa indicates that the hominins at Dmanisi were among the earliest H. ergaster populations to have evolved from H. habilis.
Further direct