Homo erectus (and Homo ergaster?)

Homo erectus first emerged in the fossil record after about 1.8 Mya. Characteristics which set this group of hominids apart include:

• supraorbital torus (extremely heavy brow ridge)
• occipital torus
• receding forehead (in comparison to modern humans)
• high degree of postorbital constriction
• less prognathic face
• teeth smaller in proportion to the rest of the skull
• very thick cranial vault bones
• sagittal keel
• large brain (approximately 900-1100 cc)

The increase in brain size from a H. habilis range (600-750 cc) marks a trend in human evolution which selected for increased cognitive abilities. Just as behavioral differences between H. habilis and the Australopithecines existed, so indeed do behavioral differences distinguish H. erectus from earlier species. The introduction of a new stone tool technology loosely coincides with the emergence of the first H. erectus fossils. This tool industry has been called the Acheulean tool industry.

The Acheulean handaxe suggests a higher degree of behavioral sophistication in its makers due to its standardization and bilateral symmetry. The consistency with which the same teardrop-shaped axe is found in Acheulean sites provides evidence for a mental image in the design and manufacture of these tools. Additionally, the degree of symmetry and spatial organization suggests that H. erectus was cognitively capable of adopting different perspectives as well as holding these different perceptions in memory during the tool's manufacture.

The Acheulean industry is found wherever H. erectus migrated, except for the Far East. It is unclear why Acheulean tools were not utilized there; perhaps it was not of necessity, or maybe a different material was used in lieu of stone tools. Or, perhaps these populations just never learned how to make Acheulean tools before migrating out of Africa. Also, while the general skeletal characteristics listed above describe Homo erectus in relation to other hominids, there is a good deal of morphological variability within this taxon, from west to east (see below for further examination of this topic).

The functional significance of the Acheulean tool industry has been debated, and several possibilities have been proposed:

1. butchering large animals
2. digging up resources found in the ground
3. use as missiles against prey and/or predators
4. stripping bark to get at edible layers
5. use as "flake-dispensers" rather than tools

Again, while the functional use for many of these tools is uncertain, the industry remained constant for about 1 million years.

The First Migration

H. erectus was the first hominid to successfully migrate out of Africa to neighboring regions (click here to see a map of H. erectus sites). Fossil specimens attributed to this species have been found as early as 1.8 mya at various sites, including Dmanisi (Republic of Georgia), Modjokerto (Java), and Longgupo Cave (central China). These indicate that H. erectus was able to migrate and successfully colonize other regions, including some in temperate environments. Evidence for the controlled use of fire may have allowed them to exploit these colder, increasingly seasonal environments.

At 1.5 - 1.6 mya, the sites of Swartkrans (S. Africa) and Koobi Fora (E. Africa) provide evidence for fire, although difficulties arise in determining whether or not the fires were deliberately manipulated by H. erectus. A site in China (Zhoukoudian) provides the earliest undisputed evidence, although that site dates to approximately 500,000 years ago.

Archaic H. sapiens

From approximately 400 - 200 kyr ago, another group of hominids emerged in Africa and Europe. Lumped into a group known as archaic H. sapiens, these specimens exhibited a further increase in cranial capacity (pictured at left is an archaic H. sapiens from Kabwe, Zambia). A higher forehead and reduction of some of the heavier morphological features (e.g., browridge, occipital torus) distinguish them from earlier H. erectus groups.

Neandertals

The Neandertals represent a highly specialized, highly derived European offshoot that coexisted with populations of anatomically modern H. sapiens. Recent genetic evidence suggests that gene flow between populations of modern humans and Neandertals was minimal. This may shed some light on the issue of the rather sudden disappearance of Neandertals in Europe, an occurence which has traditionally attributed to the arrival and colonization of H. sapiens sapiens.

Characteristics of Neandertal skeletons include:

1. very large brains (larger than modern humans)
2. rounded, elongated braincase
3. very robust musculature
4. protruding facial skeleton; large noses

Additionally, Neandertals shared a specialized tool kit known as the Mousterian industry, a Middle Paleolithic industry.

Mousterian tools exhibit a technological advance over Early Stone Age/Lower Paleolithic technologies in the efficient use of raw materials. Tool kits included up to 40 different types, many of which appear to have had specialized functions. Additionally, tool manufacture was based on the Levallois flaking technique:

The Levallois flaking technique is performed in three steps, shown in the above diagrams: preparation of the core circumference radial flaking, preparing the surface of the core detaching a flake from the prepared surface Production of tools in this fashion is very difficult in comparison to Acheulean industries, requiring a much higher degree of preparation and planning. While flakes produced in this manner were used in sophisticated ways (e.g., composite tools), the technique itself produces a relatively high amount of waste.