The First African Exodus The Emergence of Early Homo in Europe and Asia

The sabertooth big cat had been dead for only a few minutes and had not yet attracted attention from the roaming scavengers of the sky and savanna plains. Quietly the hominin approached the cat. It was most unusual to be the first on the scene of such a prize, a large cache of fresh meat. Looking around she picked up a number of large volcanic rock fragments and begun to hammer out a number of crude but very sharp flakes. She looked around to make sure that no other carnivores were approaching. Seeing no sign of approaching danger, she quickly cut into the still-warm carcass. Tearing through the body she came across the liver and proceeded to cut into it, pulling it free. Just as she succeeded in doing this, she was startled by a hyena, who began to circle around her. This meant trouble. She knew that close by would be the rest of the pack. She gathered up the meat she had managed to scavenge and quickly left the cat's carcass to the hyena. She had managed at least to retrieve a small portion of meat, some of which she could share with members of her group. It made no sense to traverse the savanna carrying quantities of fresh meat, the smell of which would surely attract any number of predators. She sat down beside a small tree for cover and proceeded to eat the portion of liver she had managed to retrieve.

It was almost three weeks since she had came across the dead big cat. Now she lay dying a terrible death. The group had been pleased with her prize, and that night some meat was added to their diet of tubers, nuts, and other plant material. Within hours of consuming the liver, she had begun vomiting as well as developing an intense headache, which progressively got worse. Within days her joints had begun to ache and she had uncontrollable diarrhea. It was not long before her skin started to peel and blood began oozing from her pores. The members of the group cared for her as best they could. They managed to keep her alive for a few weeks, but the end was near. Some in the group knew that she must have consumed the easily eaten soft flesh; they had seen this condition before in others long ago who had eaten it. Soon she was dead, and the group moved on, leaving her body to the elements.

Now she is known as KNM-ER 1808, and her discovery and the interpretation of the pathology of her skeleton has given us important clues to early hominin behavior. She represents an early species of our own genus, Homo, known as Homo ergaster. She lived and died in East Africa around 1.5 Ma. Her bones tell us that she was a likely victim of hypervitaminosis A (Walker et al., 1982; Walker & Shipman, 1996). A study of KNM-ER 1808 by Alan Walker and colleagues demonstrated that shortly before death, her bone had become increasingly brittle, fibrous, and coarse-textured, suggesting an increased breakdown within the bone-forming cycle. Today this pattern is seen in rare but severe cases of hypervitaminosis A. The highest concentration of vitamin A is in carnivore liver; because KNM-ER 1808 was the victim of severe vitamin A toxic poisoning, she most likely had eaten carnivore liver. She appears to have been a victim of the early introduction of increased meat supplementation into the early hominin diet, a period of trial and error (Walker et al., 1982). Later hominins would know better and not consume this toxic part of an animal carcass. Her death also tells us something of her life.

Walker realized immediately the significance of his pathological interpretation of KNM-ER 1808 for early hominin behavior — "Someone else took care of her" (Walker & Shipman, 1996: 134). There is no way she could have survived alone for long in the African savanna. She would quickly have succumbed to the roaming carnivores. We know she survived for some time because it would take at least a few weeks, if not months, for this pathology to show up in her bones, so someone must have been feeding her and protecting her from the carnivores, including hyena packs. Perhaps more importantly, this someone must have had some way to bring her water, requiring some form of water "container," which requires planning. It is unlikely that she would be near a watercourse because this would be a major focus area for carnivores looking for a drink and a feed. The group dynamics of early Homo must have been based on some form of mutual support.

It is with the emergence of our own genus that we see a significant expansion of the brain and a dietary shift toward an increasing reliance on meat. The smaller inverted funnel-shaped rib cage of the proto-australopithecines was adapted to house a large gut and intestines, so as to process large quantities of plant material that made up much of their diet (Aiello & Wheeler, 1995). With the emergence of early Homo, the potbelly of the proto-australopithecines gave way to a more slim physique, for these humans relied on a more varied diet, including meat; they had no need for a large gut and intestine, and their body proportions reflect this (Aiello & Wheeler, 1995; see also Bunn, 2002; Schoeninger et al., 2002). Overall the earlier, more primitive proto-australopithecines were bipedal "great apes." The same applies to the earliest representative of our genus, H. habilis, as well as the even more specialized hominin Paranthropus. It is from around 2 Ma that we see within the fossil record a major physical and behavioral shift with the emergence of Homo ergaster in East Africa.

The dietary and behavioral shift to an increased focus on meat eating within the earliest representatives of Homo was not a simple matter. It probably required a major change in group dynamics involving cooperation and coordination of individuals, an increased dependence on tool technologies to help in meat acquisition and processing (specimens of H. ergaster are associated with the primitive Oldowan stone tool technology), and certainly a major reconfiguration in hominin gut morphology in order to process associated fat and meat fibers. As discussed in the previous chapter, it is likely that some proto-australopithecine species incorporated meat into their diet, but it was probably not an important component of their diet (Cameron, 1993a; Cameron & Groves, 1993). Indeed, the major dietary focus of these hominids and the hominin species within Paranthropus is usually associated with a dependence on eating fruit with hard nuts and seeds (see discussions in Kay & Grine, 1988; Schoeninger et al., 2002). We are still debating the degree to which Australopithecus incorporated meat into its diet, though the recent isotopic studies of Sponheimer and Lee-Thorp (1999) suggest that Australopithecus (specimens dating to around 2.5 Ma) consumed large quantities of animal tissues from large grazing animals. They conclude that it was how Australopithecus and Homo exploited their food sources, as much as the exact sources they used, that distinguished them: Stone tools, in particular, enabled Homo to disarticulate the skeletons and get at the marrow.

If this is true, it appears that while Australopithecus had yet to develop the complex behavioral and technological abilities of early Homo, they must have shared at least the incipient beginnings of the specialized gut morphology in order to incorporate increasing degrees of meat into their diet.

The primitive hindgut morphology observed in most primates is related to processing simple carbohydrates obtained from fruit and proteins from leaves, whereas carnivores obtain their energy source from meat fats (Strait et al., 1997; Fleagle, 1999). In hindgut fermenters, the proteins associated with folivory go into the stomach, but they do not break down immediately because they are composed of indigestible fibers requiring a large fermentation chamber. The stomach contains a large number of bacterial colonies to break down these fibers over time, and hindgut fermenters have very large colons and stomach chambers (Chivers & Langer, 1994; Fleagle, 1999; Schoeninger et al., 2002). An increased dependence on meat eating, however, also means an increase in nitrogen, which is toxic to the foregut bacteria. And a corresponding decrease in levels of fiber means that there is a significantly increased rate of colonic twisting (Schoeninger et al., 2002). As hominins became more carnivorous, the stomach and colon would have been reduced in size, while the intestines must have been significantly more developed because it is within the foregut (small intestine) that fat digestion occurs.

While the question of why this shift to increased meat eating occurred does not necessarily require complex explanations (in order to take advantage of a rich dietary niche not previously occupied by hominid groups), the question of how it happened is far more difficult to answer. Perhaps the most elegant model proposed is that recently provided by Bunn (2002) and Schoeninger et al. (2002). They emphasize that there was a transitional phase, where an increase in the level of tree-fruit pulps would avoid problems of the colonic twisting, while lipid-rich food items obtained from seeds and other nonmeat materials emphasized the increased ability of the lipid-digesting section of the small intestine. At some point there was a further reliance on lipid-rich foods (including meat) to obtain energy requirements, with corresponding decreases in fiber lipids, resulting in a larger foregut and smaller caecum. Associated with this is the increased development of stone tool technologies, such as grinding stones, in order to process those foods that could not be directly consumed given the switch to an increased foregut. These technologies would enable seed coat removal, enhancing access to seed protein by removing digestion inhibitors. The increased tool technology comes with the emergence of Homo, which unlike its Pliocene forebears was now able to take advantage of a much broader dietary base (see Bunn, 2002; Schoeninger et al., 2002).

There is no definitive evidence that Paranthropus was a habitual tooluser or tool-maker; its food-processing abilities tend to be associated with a primitive pattern of oral preparation, which is emphasized further by its robust facial structure and enormous grindstone-like premolars and molars. Selection pressures appear to have focused on increasing its robust skull and dental complex, so the ancestral member of this robust lineage, P. walkeri, while probably sharing the "transitional" phase in gut morphology (passed on from its late Miocene/early Pliocene ancestor), did not revert to meat eating but emphasized other lipid-rich resources, probably a specialized diet of hard fruits, hard seeds, and other abrasive foods. This dietary overspecialization, in the face of the habitat conflict with other, nonrobust hominin groups, must have contributed to the eventual extinction of the robust hominins.

It is clear that by the time H. ergaster appears in the East African fossil record, moderate levels of meat eating had been incorporated into the diet. Specimen KNM-ER 1808 provides evidence that this was not always a successful adaptation and that some form of "trial and error" was still being invoked. It was the broadening of its dietary base, and associated behavioral adaptations as well as increased dependence and development of stone and nonstone technologies (again demonstrated by the protection, feeding, and help given to the individual represented by KNM-ER 1808), that enabled members of this species to increase their territorial range and thus to increase access to resources.

While H. habilis and H. ergaster are both thought to have manufactured the primitive Oldowan tool technology, it may be that H. ergaster was the first to become increasingly reliant on it, while H. habilis was an infrequent user of stone tools. Or it may be that H. ergaster alone was responsible for their manufacture. The South African hominin StW 53 specimen from Sterkfontein Member 5 (dating to around 1.5 Ma), which until recently had been tentatively allocated to H. habilis, is associated with Oldowan-like chopping tools (see Brain, 1981). However, Kuman and

Clarke (2000) propose to reallocate this specimen to Australopithecus. They argue that it is part of a secondary deposition and thus was not necessarily deposited at the same time as the tools. If this is so, the jury is still out with regard to H. habilis as a tool manufacturer. So far, only H. habilis and P. boisei are known from Olduvai Gorge Bed I, where Oldowan tools are abundant; but there are so few specimens that at any moment H. ergaster or some unexpected species may turn up there. While early demes of H. ergaster are associated with Oldowan technology (or Mode I technology), Acheulean tools (or Mode II) are first associated with later populations of H. ergaster from Konso, Ethiopia, around 1.4 Ma (Figure 6.1). This new tradition is defined by biface instruments, much more elaborate than those of the Oldowan tradition. This new toolkit consisted of hand axes, cleavers, and picks and must have involved considerable forethought and planning, for the tools represent a predetermined design rather than "blades" struck from a core. This demonstrates that new tool traditions — technologies need not be correlated with the appearance of new hominin species.

Ovate hand axe

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