The Human Fossil Record, Part 10b: Homo erectus in Asia, Cont’d
Note: Yesterday and today, Dr. James Kidder continues to tell the story of the evolution of creatures on our own small branch of the primate family tree, the hominins. Kidder’s previous post in the series looked at fossil evidence helping anthropologists answer the question, “When did our ancestors first start exploring beyond the African continent?” and focused on sites in Europe and the Middle East. Here Kidder turns our attention east and describes the discovery Homo erectus.
In yesterday’s post, I discussed Eugene Dubois’ 1891 discovery of Homo erectus in Java, and some of the subsequent discoveries of other remains throughout Southeast Asia and into China. Today, we’ll look at the Zhoukoudian site, which contains perhaps the largest Homo erectus cache of fossils in existence at any one site. Not only did the caves provide a remarkable number of remains, it also provided one of the greatest mysteries of paleoanthropology.
In the late 1920s, vertebrate paleontologist Davidson Black, who was working at the Cenozoic Research Laboratory, began an excavation in the hills outside what was then known as Peking (now Beijing). Local townsfolk had brought Black bones to him that they claimed were those of “dragons.” These turned out to be extinct fauna. Quickly, Black discovered some hominin mandibles, some cranial fragments and one complete calvaria. He named the new species Sinanthropus pekinensis, or Chinese man from Peking. Black continued the excavations until his death in 1934, whereupon Franz Weidenreich was brought in. A trained anatomist who had just finished up a visiting professorship at the University of Chicago, Weidenreich found an additional five complete calvaria as well as several partial crania and fragments. He immediately recognized similarities between what Dubois had unearthed and what was being found at Peking: individuals with long, low crania, large brow ridges and large faces.
Weidenreich continued to excavate through the mid-1930s, but in 1937 the Japanese invaded the north part of the country and many Chinese fled south to escape the oncoming armies. Sensing that the trouble would eventually reach Peking, Weidenreich readied all of the material for transport out of the country: he completed high quality plaster casts of the fossil remains and took them with him to New York. The original fossils he locked away for safekeeping.
In 1941, as conditions in China continued to deteriorate, the decision was made to move the original fossils, which were placed in a set of footlockers and given to a garrison of U.S. solders stationed in Peking. The plan was for them to be transported to the port city of Qinhuangdao, where they were to be loaded onto the U.S. Benjamin Harrison. What then happened is not entirely clear. The Japanese army captured the garrison of marines and the bones seemingly vanished. No one ever saw them again, and to this day the whereabouts of the fossils remain a mystery. Some believe that they went back to Japan with the Japanese army, others think that they became scattered among the local inhabitants of the area, and still other suggest that they ended up at the bottom of the ocean, never to be seen again. In 2005, the Chinese government began a program to locate the original bones.
The Zhoukoudian site yielded an amazing amount of material: twelve total crania of which six were almost complete, as well as a large collection of mandibles and hundreds of cranial fragments (Figure 7). The cranial capacity of these individuals ranges from 915 to 1225 cc, making them larger than the majority of the Southeast Asian individuals. But nearly as important as the fossils themselves, researchers found numerous stone “cleavers” and four layers of ash, reflecting the use of fire. All in all, there seems to have been a continuous occupation of the cave from around 600,000 to 200,000 years ago, spanning thirteen layers and some forty meters of deposits. Along with the crude implements, hundreds of mammal species are represented by remains in the cave, many of the bones having distinctive cut marks on them. This suggests that the occupants of this cave could (and did) hunt many different species for food.
Homo erectus and the Hand Axe:
While the archaeological record of tools for the Southeast Asian Homo erectus sample is extremely thin, some Chinese sites have provided artifacts. (Schick & Zhuan, 1993). Uniformly crude and not as developed as the Acheulean mode tools in East Africa, these bifacially-worked chopping tools have been referred to as “cleavers” by some researchers (figure below). There is considerable variation in size and shape, however, and Lycett has argued that there are regional variations in biface design and construction that can be attributed to the demands of different environments (Lycett, 2008). Interestingly, it is also clear that, over time, these tools became more uniform, resembling the hand axes that are found elsewhere. This suggests two strong possibilities: first, that specific functional necessities were the driving force behind their shape, and that these functional constraints necessitated a similarity in design between groups; or, second, that “technology swapping” between populations was occurring.
Although these “cleavers” appear in numerous places in the Chinese record, there is a sharp break between them and the well-made hand axes of Africa, Southwest Asia and the Indian sub-continent. This break is referred to as the “Movius” Line, named for the researcher who first noticed the pattern. It has always been a source of puzzlement to archaeologists, but recently, some researchers have suggested that this demarcation exists because the Chinese Homo erectus populations possessed a raw material alternative for creating the complex tools they needed: bamboo. Bar-Yosef and colleagues have shown that with less effort and time required to make them, bamboo points can be created that are nearly as strong as and easier to use than stone ones (Bar-Yosef, Eren, Yuan, Cohen, & Li, 2012).
Beyond Homo ergaster: How many species of Mid-Pleistocene Homo?
One of the persistent problems of hominin studies when we get to our own line is attempting to determine how many species coexisted. As we have seen previously, there was even disagreement about how many species were represented in Eastern Africa, with Homo rudolfensis and Homo ergaster.
Historically, many archaeologists have held that Homo erectus was the hominin that colonized the Old World, and that this colonization took place between one and two million years ago. During the 1970s and 1980s, paleoanthropological thought held that Homo habilis followed the reign of the australopithecines, and was in turn followed by Homo erectus. More recently consensus has emerged around the idea that there was further speciation in those populations that ended up in Europe and Asia. Whether one accepts one species (H. erectus) or two (H. erectus and H. ergaster), there is, as Ian Tattersall describes, “a relatively cohesive subset of the family Hominidae.” (Tattersall, 2007)
Indeed, one is struck by the unity in morphological features that make up Homo erectus/Homo ergaster in all parts of the Old World. Rightmire (Rightmire, 1998) has consistently argued that the traits used to differentiate Homo ergaster from Homo erectus are lacking and that it is best to simply use the name Homo erectus to describe all of the middle Pleistocene hominins between about 1.6 million and 300,000 years ago. Antón suggests the following traits that characterize the species as a whole: a cranial vault ranging in volume from approximately 700 to 1200 cc; a low, sloping forehead and sharply angled rear; a large, single brow ridge over the eyes; and sharp muscle markings on base of the vault with very thick cranial bone. (Antón, 2003).
Cranial morphology is remarkably static through time as well (Kidder & Durband, 2004), with little change for hundreds of thousands of years. Differences that are found do not constitute trait polarities (presence or absence of a particular feature), but are differences in overall dimensions within a consistent general type, such that it is reasonable to assign these distinctions to regional genetic drift.
On the other hand, Wood has made the argument that, while it is reasonable to assign the taxon Homo erectus to the material in Asia, it is not reasonable to do so for the African remains: the Asian samples are marked by the presence of traits such as the sagittal keel (a ridge of bone on the top of the head, visible on Figures 1 and 4), the angular torus and thick cranial bone, while these features are not as evident in the African examples. Wood has suggested that the earliest fossils from Africa—originally designated Homo erectus—be called Homo ergaster, instead, a convention I adopted for the previous post in this series. At some point, however, a group or groups left Africa with some of these traits present, and the best explanation for their presence in both the Chinese and South East Asian populations is shared retentions from an ancestral population.
Homo erectus and the Created Order
At some point we must consider Homo erectus from another perspective, as well. It has been argued by those opposing evolution in general and human evolution in particular that the australopithecines represent nothing more than aberrant apes (Morris, 2002). While such an argument does not bear up under scrutiny even with regard to australopithecines, it certainly cannot be used to describe Homo erectus in light of the extensive material we have for this species. Not only is Homo erectus morphologically stable through time and across geographical space, it is also clear that these hominins are considerably more advanced than australopithecines (Figure 9). The crania of Homo erectus are longer, higher and considerably larger in volume; the face is more pulled in and less scooped. These are individuals that are creating complex stone tools, which are economical and efficient. In China, they are also controlling fire, an invention that completely changes how the day may be organized, and also expands the repertoire of what is edible. There is evidence for the controlled use of fire at both Lantian and Zhoukoudian and, considering the evidence at Gesher Benot Ya’aqov, it appears that as Homo erectus moved east, they brought fire with them.
While not completely human, it is clear that Homo erectus were hominins practicing many of the behavioral patterns that we identify as human, and were getting closer to being human.
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