Implications for Behavior

What do the various lines of evidence mean in terms of what Homo erectus actually did at Zhoukoudian? Some archaeologists have suggested that the apparent sameness of the stone artifacts from the lowest levels of the cave site to those at the top show that Homo erectus was a very slow-witted species. Others have pointed out that the hand ax, a tear-shaped stone tool with a characteristic double-faced cutting edge, never made it to China, even though it was characteristic of much earlier Homo erectus sites in Africa. Was Homo erectus at Longgushan particularly slow on the uptake, or are there other explanations?

The raw material for stone tools at Longgushan may provide part of the answer. Quartz is an abundant crystalline rock that gives a sharp edge when broken, but it is a notoriously poor stone for flaking into large or complex tools. Quartz is shot through with cleavage planes that cause the stone to break into unpredictable shapes, frustrating even the most adept or artistically ambitious of stone-tool knappers. The Longgushan homi-nids had to settle for small flakes of quartz, which they used for slicing and for scraping muscle off bone. For bigger jobs, such as cutting through the rib cage of a deer carcass, they used a hefty chopping tool made of sandstone. Sandstone occurs in the Zhoukoudian region, but it is not a crystalline rock—it does not fracture like thick glass or give a sharp edge. But for cracking ribs by using brute force, it is effective. Sandstone just cannot be made into a recognizable bifacial hand ax. Thus, we do not think that too much should be made of the perceived deficiencies of the Longgushan stone tools because of the natural geological limitations of Dragon Bone Hill. We believe that the archaeology of Longgushan reflects the general capabilities of the species Homo erectus, modified to fit local conditions.

There are other explanations for the rarity of bifacial tools in the Pleistocene Epoch in China. Paleoanthropologist Geoffrey Pope proposed that bamboo tools could have been used extensively,18 perhaps in a way that substituted for hand axes, but evidence of them would not likely be found in fossil sites. The problem with this explanation in the case of Longgushan is that bamboo today grows only in the south of China, nowhere near Dragon Bone Hill. Inferences from the fossil fauna also make it doubtful that southern Chinese flora ever extended up to northern China. The panda (genus Ailuropoda), which lives on bamboo and is common to southern Chinese Pleistocene sites, is unknown in northern China. Although quite a few fossil trees have been identified in Longgushan, bamboo and similar tropical species are not among them.

In the 1940s archaeologist Hallam Movius first proposed a line of demarcation that separated the hand ax—containing sites of Europe and Africa from the Asian sites that lacked such artifacts.19 The so-called Movius Line was located in Central Asia and extended down into the Arabian Peninsula. The line's location has always defied a reasonable explanation, but the general opinion has been that it represented a cultural division line or an ecological boundary. Hominids to the west were thought to have used hand axes, and hominids to the east used chopping tools. Recent archaeological research, however, has confirmed that though less abundant than in African sites, hand axes are found in China.20 Sometimes, as in the case of Longgushan, there can be a mineralogical reason that hand axes have not been made. In other cases the reason is less clear. But underlying the entire issue is the fact that we still do not even understand what a hand axe was used for. Perhaps Asian Homo erectus did not appreciate its advantages either and found that a single-edged chopping tool did the job just fine.

Archaeologist David Hopwood has recently analyzed Homo erectus stone tools and the raw materials from which they were made.21 He measured complexity of tool manufacture and the spatial aspects of sites, and from how far stone was brought to make tools. His findings show that early Homo erectus was quite similar in both Africa and Eurasia. About eight hundred thousand years ago in Africa Homo erectus sites became highly clustered, a pattern that Hopwood believes indicates a greater degree of social organization and social interaction. In Asia, however, he found a different pattern of regularly spaced sites that implied to him no substantial social interchange and perhaps even avoidance in the period between eight hundred thousand and six hundred thousand years ago. Asian tools show much more local derivations than African ones, while at the same time African tools were significantly more complex and raw materials there were being transported long distances. Implications of these intriguing findings remain to be investigated.

The stone tools that Homo erectus wielded at Longgushan were not its state-of-the-art technology. Fire was. If we imagine what it might have been like, eking out a life in Ice-Age China with only stone tools in or near a cave with large predators, survival seems an iffy prospect. Add fire to the equation, however, and we might feel that chances for survival were significantly enhanced. Indeed, paleoanthropologists have for many years generally believed that fire was a prerequisite for hominids to colonize the higher, colder latitudes of Eurasia as they expanded out of Africa.

A corollary of this idea is that the first evidence of fire should be found in early archaeological sites in Eurasia. Research by archaeologists J. D. Clark and J. W. K. Harris in very early archaeological sites in Africa beginning in the 1970s challenged this idea.22 Clark and Harris found areas of baked clay on the fossil savanna landscape of Koobi Fora and Chesowanja, Kenya, dated to an astonishingly early 1.7 million years ago, at the very dawn of the species Homo erectus. Recent research on the geochemical aspects of Clark and Harris's data by Ralph Rowlett of the University of Missouri has provided support for this controversial hypothesis.23 We think the data are solid and we agree that fire was tamed early by hominids. But if that is so then the original use of fire by hominids must have been for other purposes than to warm themselves against the Ice-Age cold and to light the interiors of dark caves. Hominids likely used fire in their interspecies competition for food and space on the African savanna. Those lessons were simply extended to different species and different contexts in Eurasia.

The evidence from Longgushan is compelling in indicating that the cave was primarily a hyena den that Homo erectus occasionally shared with a number of other species of carnivores, birds, bats, and rodents. Fire was first and foremost a means by which Homo erectus could effectively compete with these other species and hold its own in the hurly-burly of Pleistocene China. Cooking was only a by-product of this adaptation and rendered certain foods that were difficult to process, such as a horse head, much more accessible and palatable. But it is likely that hominids, like their primate cousins the macaque monkeys (also at Longgushan), had a diverse enough diet without fire to survive. The warmth that fire provided was also likely a benefit in severe conditions, but the primary adaptation against Pleistocene cold was undoubtedly shelter, not fire. Small shelters probably date back to pre-fire-using Homo, again in Africa, and they would have been effective without an interior fire. In fact, without a chimney small huts can be rendered much less habitable by the smoke and soot from a fire.

The early advantage that fire gave to Homo erectus was a leg up on the competition with other species—a competition that was exacerbated by climatic changes accompanying the onset of the Ice Ages. In the next chapter we look at how both global changes in climate and local conditions at Longgushan affected the life of Homo erectus.

The Adaptive Behavior of the Not-Quite-Human 105 Hunter, Gatherer-Hunter, or Scavenger?

Homo erectus used to be thought of as the first hominid to have engaged in big-game hunting—running down and dispatching animals larger than themselves. Part of this opinion was rooted in the Western cultural memory that hunting was primitive, predating agriculture, and was the way our early ancestors made a living. The evidence of this mode of life was the large animal bones found at such archaeological sites as Torralba and Ambrona in central Spain, investigated by paleoanthropologists F. Clark Howell and Leslie Freeman beginning in the 1960s.24 Here mammoth bones were found in association with Homo-erectus-aged stone tools. Homi-nid bones were never found, but the association of big-game hunting stuck with Homo erectus nevertheless.

A new generation has questioned the big-game hunting interpretations of Torralba-Ambrona and other early hominid sites. These archaeologists point out that the elephant bones and stone tools merely showed that hominids had cut up large animals and presumably eaten them. It said nothing about how the hominids had come into possession of the carcasses in the first place. Among the most powerful tools that these researchers used was the scanning electron microscope (SEM), with which they examined the surfaces of the bones at archaeological sites. SEM photomicrographs became important for distinguishing the various marks left on bones—from shallow parallel scratches resulting from trampling by antelopes to deep U-shaped grooves made by the teeth of carnivores, to the repetitive closely spaced gnaw marks of rodents, to the V-shaped and sharply incised cut marks left by hominid stone tools. Analysis after analysis of early hominid sites showed that cut marks almost invariably overlay bite marks, indicating that carnivores had eaten part of the meat first, and had presumably hunted down the animal initially. Zhoukoudian fit into this pattern of reinterpretation of big-game hunting. Both Lewis Binford's bone damage studies and our own have supported the interpretation that Homo erectus at Longgushan were scavengers and not hunters.

Support for the scavenging hypothesis comes from an unlikely source. Parasitologist Eric Hoberg and his colleagues at the U.S. Department of Agriculture studied the three species of tapeworms that infect the human species. In comparing them to all the known species of mammalian tapeworms, they found that they were closest to the tapeworms that infest hyenas, felids (lions and tigers), and canids (dogs and wolves). Taenia solium, known as the "pork tapeworm," is the primary species infesting humans. It shared a recent common ancestor with the hyena-infesting species, and according to molecular studies, they diverged evolutionarily between 1.7 million (the beginning date of Homo erectus) and 780,000 years ago.25

Taenia saginata (the "beef tapeworm") and Taenia asiatica (the "Asiatic tapeworm") are other tapeworms that infest humans and, quite surprisingly, they also diverged at about the same time from the tapeworm that infests cats. Hoberg hypothesized that the tapeworms rode out of Africa in their migrating hosts (prey animals like pigs and antelopes) and were picked up first by early hominids "when they started eating more of the same worm-bearing meat as big cats and hyenas did."26 Both the timing and the species involved make sense from the standpoint of the paleontological and archaeological evidence for scavenging from Longgushan. But the tapeworm data add substantially to the story.

Homo erectus can only have contracted infestations of these tapeworms, living in different intermediate hosts, if they first began to eat these new mammal species, or began to eat much more of them, at 1.7 million years ago. The fact that three separate and independent species of tapeworms from three separate mammalian species (presumably a pig, a bovid antelope, and an unknown Asiatic mammal) adapted to the hominid digestive tract at the same time strongly implies that meat from different species became a much more significant part of the hominid diet at this time. These data alone could be explained by positing hominids eating host prey animals and the infesting tapeworms diverging and adapting to live in the hominid digestive tract. But the problem becomes a multispecies ecological puzzle when we consider that carnivores were also eating the same prey species, thereby sharing their parasites. And not once, but thrice. How did the tapeworm species that began to parasitize hominids also share ancestry with the species that infested carnivores?

A solution to the puzzle may be to imagine the world from the standpoint of the tapeworm. Its eggs are eaten by a prey animal, such as a deer, and then hatch inside the digestive tract. Larvae burrow through the intestinal wall and enter the prey animal's bloodstream. Larvae then go into a quiescent, encysted state called a cysticercus and become embedded in the deer's muscle. There they wait to be eaten by a meat-eating species, such as a hyena (the definitive host), in whose digestive tract they can finally realize their potential and develop into adult tapeworms. It must be a lonely and risky life for most tapeworms, many of whom may never be rescued by a marauding carnivorous species from their larval state of suspended animation. And even if their intermediate host mammal is killed and eaten, imagine the tapeworm's disappointment when, finally freed from its fleshy tomb, it fails to survive in the intestines of a foreign definitive host such as Homo erectus. Natural selection would be expected to favor a tapeworm species that was adaptable and could survive in various common intestinal environments. It is most reasonable to conclude that three different tapeworm species, originally adapted to specific intermediate and definitive hosts, speciated about 1.7 million years ago to become generalized parasites who could take advantage of a new digestive environment—that of Homo erectus. This is independent evidence that Homo erectus had adapted to a diet that contained more meat than previously, that the species eaten were varied, and that a close ecological relationship with mammalian carnivores existed.

The tapeworm evidence adds significant detail to our understanding of Homo erectus and fire. A close ecological relationship between Homo erectus and large mammalian carnivores, which we know from other evidence also ate hominids, could only have been made possible by the hominid possession of fire. Fire would have been crucial in enabling hominids to obtain meat predictably by scavenging because it was only in this manner that hominids could ever have displaced larger, fleeter, stronger, clawed, and fanged competitors. And tapeworms yield yet another clue about the use of fire. Only when meat is eaten raw or very undercooked do tapeworm cysticerci survive to infest a human digestive tract. We may surmise that in many cases Homo erectus ate meat the same way that the carnivores from whom they scavenged ate it—raw. If meat was cooked at Longgushan, Homo erectus must have preferred it rare. Otherwise the tapeworm species would never have survived to adapt so well to the hominid digestive tract.

The picture of Homo erectus culture that Longgushan preserves is a primitive one, a world apart from our own. Nevertheless, erectus culture was a powerful adaptation for its time. Using rudimentary stone tools and a tenuous control of fire, and having a dependent scavenging relationship with dangerous large carnivores, Homo erectus did more than eke out an existence in Pleistocene. It flourished, multiplied, and expanded its range. The ecological conditions that attended this unlikely evolutionary transition help explain how and why these adaptations evolved. We next look at erectuss world.

CHAPTER 6

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  • Dahlak
    What was the implications of social organizations for early hominids?
    2 months ago

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