chapter thirteen: From Hominin to Homo

Chapter Review

The Lower Pleistocene

A much more human-like hominin evolved in Africa approximately 1.8 million years ago (mya). Fossil specimens representing Homo ergaster have been found in a number of places in Africa, including Olduvai Gorge in Tanzania, Lake Turkana in Kenya, and Swartkrans in South Africa. Some of the anatomical features of this hominin include the following:

Supraorbital torus (extremely heavy browridge)
Occipital torus
Receding forehead (compared to modern humans)
High degree of postorbital constriction
Less prognathic face than previous hominins
Teeth smaller relative to the rest of the skull
Very thick cranial vault bones
A larger brain (on average 800 cubic centimeters [cc])
Reduced sexual dimorphism

Homo ergaster continued to use Oldowan tools (see Chapter 12), though between 1.6 and 1.4 mya new tools begin to appear in the fossil record. Known as bifaces, these tools were both more complex and more standardized in form than the Oldowan tools.

The Acheulean hand ax suggests a higher degree of behavioral sophistication in its makers due to its standardization and bilateral symmetry (Figs. 13-1 and 13-2). The consistency with which the same teardrop-shaped ax is found in Acheulean sites provides evidence for a mental image in the design and manufacture of these tools. In addition, the degree of symmetry and spatial organization suggests that H. ergaster was cognitively capable of adopting different perspectives as well as holding these different perceptions in memory during the tool's manufacture.

[Scan figure 13.8 from 4e text and insert here].
[caption]Figure 13.1 Acheulean hand axe. Credit: W.W. Norton.
The functional significance of the Acheulean tool industry, and the handaxes in particular, has been debated, and several possibilities have found explanatory traction:

As missiles against prey and/or predators
For butchering large animals
For stripping bark to get at edible layers underneath
As “flake dispensers” (knocking off smaller flakes for use as tools)
For digging up roots and other difficult to extract foods

While these possibilities are all intriguing, evidence that they were used for animal butchery has begun to emerge. And the industry stayed fairly constant for about 1 million years!

Behaviorally, H. ergaster probably ate meat, may have controlled fire, and surely practiced complex foraging. In short, they represent a significant departure from the australopithecines in their anatomical and adaptive development. A remarkable fossil find on the west end of Lake Turkana in Kenya by the Koobi Fora team of paleoanthropologists illustrates well the changes that this new hominin represents. In 1984 the team uncovered the nearly complete skeleton of a boy who probably died at about the age of 12. Already, this individual (KNM-WT 15000) was about 5’4” tall! If Homo ergaster patterns of growth were more similar to the growth patterns of modern humans than to those of the australopithecines (a not altogether safe assumption), he would have grown up to be about 6 feet tall, well within a modern range for height. He also had very modern limb proportions—longer legs and shorter arms—as compared to the long-armed australopithecines. Further, this find and others suggests that sexual dimorphism was much reduced by the time Homo ergaster evolved.

Additionally, Homo ergaster fossils appear in Eurasia at about the same time they emerged in Africa (around 1.7 mya). In 1999, archaeologists from the United States and the Republic of Georgia found two skulls at a site named Dmanisi in the Caucasus mountains of Georgia. The morphology of the crania is very similar to that of the African finds that are dated to the same period. This kind of migration also represents a turning point in hominin evolution. Earlier hominins lived only in warm environments; clearly Homo ergaster’s move into a cooler, drier area means that they were better able to buffer themselves against the whims of the elements.

The Early Middle Pleistocene (900,000 to 300,000 years ago)

Eastern Asia

Homo erectus, a hominin from Asia, was very similar to H. ergaster. The differences between them (mainly in certain features that highlight the greater robusticity of Homo erectus crania), though, has led many paleoanthropologists to split them into two separate species, as we do here. Fossil specimens attributed to H. erectus have been found at various sites in Indonesia and China. These indicate that H. erectus was able to habituate to other regions successfully, including some in temperate environments. The controlled use of fire may have allowed them to exploit these colder, increasingly seasonal environments.

The Acheulean industry is not found associated with H. erectus, however. It is unclear why Acheulean tools were not used; perhaps they were not needed or maybe a different material was used in lieu of stone. Also, while the general skeletal characteristics listed above for H. ergaster also describe H. erectus in relation to other hominins, there is a good deal of morphological variability within this taxon.

Africa and western Eurasia: H. heidelbergensis

In the first half of the Middle Pleistocene, another group of hominins emerged in Africa and Europe. Lumped into a group previously known as archaic H. sapiens, these specimens exhibited a further increase in cranial capacity, a higher forehead, and reduction of some of the heavier morphological features (for example, browridge, occipital torus), which distinguish them from earlier H. ergaster groups. These hominins are called Homo heidelbergensis for the German town of Heidelberg where some of their first fossils were found. It is unclear, though, whether all fossils from Africa and western Eurasia should belong to the same species.

The Later Pleistocene (300,000 to 50,000 years ago)

Eastern Eurasia

During the later Pleistocene, H. erectus and H. heidelbergensis may have co-existed in East Asia. Also at this time tool manufacture became more complex, based on a flaking technique called the Levallois.

The Levallois flaking technique is performed in three steps.

Preparation of the core circumference
Radial flaking to prepare the surface of the core
Detaching a flake from the prepared surface

Production of tools in this fashion is difficult compared to Acheulean industries and requires a much higher degree of preparation and planning. While flakes produced in the Levallois manner were used in sophisticated ways (for example, composite tools), the technique itself produces a relatively high amount of waste.

6-1

Figure 13.2 Diagram of the Levallois stone-tool flaking technique.
Image Credit: W.W. Norton.

Interestingly, during the Upper Pleistocene, Homo erectus also seems to have evolved into a very unique hominin on the island of Flores, one of many archipelagos that currently are part of Indonesia. Researchers working at a cave site called Liang Bua, in 2004, discovered the remains of a number of very very small hominins. They were only about 3 feet tall, and their brains were also tiny (in hominin terms) with a cranial capacity of around 380 cc. This addition to the hominin family tree—named Homo floresiensis after the island on which they were found—incontrovertibly shows that humans and our ancestors are subject to the same wide variety of evolutionary forces that affect all life on the planet. The island of Flores has always been isolated from the mainland, and therefore only a very few kinds of large mammals populated the island. All of them (including the hominins!) underwent a “dwarfing” process in response to the limited resources of the island.

Western Eurasia

The Neanderthals represent a highly specialized, highly derived European–Near Eastern offshoot that co-existed with populations of anatomically modern H. sapiens. Recent genetic evidence suggests that gene flow between populations of modern humans and Neanderthals was minimal. This may shed some light on the issue of the rather sudden disappearance of Neanderthals in Europe, an occurrence that has traditionally been attributed to the arrival and colonization of H. sapiens.
Characteristics of Neanderthal skeletons include the following:

Very large brains (larger than modern humans)
Rounded, elongated braincase
Very robust musculature
Protruding facial skeleton; large nose

In addition, Neanderthals shared a specialized tool kit known as the Mousterian industry, a Middle Paleolithic industry.
Mousterian tools exhibit a technological advance over Lower Paleolithic technologies in the efficient use of raw materials. Tool kits included many different types that appear to have had specialized functions.

Neanderthal Behavior and Culture

Some points concerning the behavior of Neanderthals are the following:

They had very few established campsites.
They buried their dead (e.g., Shanidar, La Ferrassie, La Chapelle-aux-saints, Le Moustier).
Many appeared to have lived short, traumatic lives.
They cared for their old and sick (for example, at La Chapelle-aux-Saints, Shanidar Cave).

Intentional burial and care for the seemingly weaker of their groups suggest that Neanderthal culture was more developed and sophisticated than the hominin species that precedes them. Although their lifestyle was marked with both climatic and behavioral hardships, they also were, perhaps, the first hominins to care for the sick and infirm, although there is debate among anthropologists about why Neanderthal individuals with severe injuries were able to survive.

Africa

Around 190 thousand years ago (kya) anatomically modern humans evolved in Africa, although the evidence is still a little sketchy. They had large crania and were very robust, sharing some features with Homo ergaster, but a few specimens dated that early appear much more modern, especially in the highness of their foreheads. They also had none of the specialized features characteristic of the Neanderthals to their far north. More solid evidence for anatomically moderns appears around 160 kya at various African sites. The technology of these possible Homo sapiens was also significantly advanced. The members of our species, though, will be fully discussed in the next chapter.

Controversy and ambiguity

The preceding descriptions seem clear enough, but underneath the basic classifications lies major anthropological controversy. Some scholars believe that the variability seen between H. heidelbergensis and H. erectus is not enough to warrant different species designations, and that the two types should be lumped into African and Asian H. erectus varieties. Other scholars hold the traditional view that Homo ergaster should also be classified as Homo erectus, though there is more and more solid evidence emerging that they were two different species. This view, that there was more than one species of H. erectus, rests on the notion that the large distance between Asia and Africa reduced gene flow to such an extent that these hominins diverged and formed new species. Alternatively, those who believe there was but a single species of H. erectus maintain that while the distances between populations was certainly great, there was not enough time for species-level differentiation to evolve.

Furthermore, there are also heated arguments over the taxonomic designation of the Neanderthals. Some researchers call them H. neanderthalensis and others call them H. sapiens neanderthalensis. Though these are only names, they reflect highly different views regarding Neanderthal's place within the human line and relationship to anatomically modern H. sapiens

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