The Human Fossil Record, Part 9: Out of Africa (The First Time)
Note: Today, 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 suggesting that the appearance of Homo ergaster in East Africa about 1.8 million years ago was a significant step towards hominins with fully modern proportions and stature. But more importantly, that more modern body (including a larger brain) seems to have come at the same time as new kinds, uses and sources of stone tools. This combination of evidence leads some researchers to surmise that these hominins were exhibiting anticipatory cognition: the ability to plan ahead for future goals, including travel over great distances to find food and other raw materials. This capability may have set the stage for additional cultural development, but also begs the question, “When did our ancestors first start exploring beyond the African continent?” This post discusses archaeological discoveries from the last 30 years that allow anthropologists to answer that question with more precision than ever before, and to fill in details of the story of how hominins developed in and outside of Africa.
Out of Africa
One of the persistent questions involving paleoanthropological research is the timing of that first migration out of Africa. Work by several researchers beginning in the 1890s had uncovered remains of hominins in both East and Southeast Asia, but because of problems understanding exactly how remains decayed or were preserved in those environments, very few concrete dates could be determined. In Europe and the Near East prior to the 1980s, there were no early hominin remains that could be dated older than 500 thousand years.
Beginning in the summer of 1999, however, the remains of six individuals—including two remarkable partial skulls, or crania—were recovered from a hilly location at the site of Dmanisi in the Republic of Georgia (see map, below). One surprising characteristic of the skulls was their primitive appearance (Figure 2). Their small cranial size of 800cc put them squarely within the early Homo range (modern humans skulls range between 1350 and 1500 cubic centimeters). Also notable was that from the back, the widest part of the head was quite low, just above the ear. In modern humans, the widest part is three-quarters of the way up from the cranial base. These characteristics, plus the shape of the eye sockets and cheeks strongly suggested an affinity to Homo ergaster (Gabunia et al., 2000).
Two characteristics were different from Homo ergaster, however. First, the skull bones were very thick, and second, they displayed a ridge of bone not found on Homo ergaster or any of its African contemporaries. This ridge, called the angular torus, is a defining characteristic of Homo erectus, the hominin that follows Homo ergaster. These characteristics strongly suggest that the Dmanisi hominins occupy a transitional status between these two forms.
In direct association with these hominins were stone tools of what is known as the Oldowan mode: scrapers, choppers and flakes (Figure 3). This tool kit was more primitive than what was associated with African specimens of African Homo ergaster and closer to what has been found at earlier Homo habilis sites. Based on Paleomagnetism and 40Ar/39Ar dating, the hominin remains at Dmanisi are estimated to be between 1.5 and 1.8 million years old, putting them within the historical range of African Homo ergaster. This suggests that the Dmanisi hominins may represent an earlier branching of the H. ergaster line, and that each line had its own independent evolutionary trajectory.
The appearance of this hominin this far north and at such an early date is striking because it suggests that an early form of Homo had learned to migrate long distances. It should be pointed out that this migration involved more of a change in location than a change in scenery. The environmental conditions at Dmanisi were dramatically different 1.5 million years ago than they are today, and analysis of the ancient climate for the hominin layers there indicates that it was a temperate savanna with small trees and brush (Palmqvist, Gröcke, Arribas, & Fariña, 2003).
Apart from the Georgian Caucasus, it appears that there was also a rapid expansion out of Africa into other areas of the Old World (defined as all continental areas except North and South America and the polar regions). This began shortly after the appearance of Homo ergaster. As Figure 4 indicates, hominins first appeared in Europe, the Near East, and Asia between 1.5 and 1.8 million years ago.
Southwest Asia (The Near East)
Because of its rich religious history, southwest Asia has always been an emotionally charged region for archaeological research. Yet it is here that scientists have found evidence of early non-African Homo. Two sites have been proposed as the earliest habitation locales in the Near East: Yiron and Erq el Ahmar, both in the Jordan Valley region of Israel. However, despite yielding primitive tools, they have not produced reliable dates.
At the site of Ubeidiya, also in Israel, several levels of habitation have been unearthed that suggest a long-term occupation between 1.5 to around 1.0 million years ago. Stone tools found at Ubeidiya range in complexity from Oldowan (such as those made by late H. habilis) to Acheulean (typically associated with H. ergaster). This indicates the presence of more advanced (and slightly later) hominins than those found in Dmanisi. Unfortunately, no human remains have been discovered at this site (Bar-Yosef & Belfer-Cohen, 2001).
Another notable site is Gesher Benot Ya’aqov, which has been recently re-dated to approximately 780,000 years ago (Goren-Inbar et al., 2000). The archaeological layers there are quite rich with thousands of tools, all of which are Acheulean in nature: hand axes and cleavers along with flake tools. The material at Gesher Benot Ya’aqov reflects a much greater complexity in behavior than at earlier sites, as well, yielding evidence of a remarkable advancement: the continual, purposeful use of fire. By examining the pattern of burned artifacts, Alperson-Afil has concluded that the small-stone waste pattern at the site reflects a controlled fire-source. The author argues that, while there are places where burned and unburned artifacts overlap, there are also clusters of burned artifacts alone. Here, he suggests “that an anthropogenic [that is, man-made] fire is the agent responsible” (Alperson-Afil, 2008, p. 1735). This conclusion has been supported by Goren-Inbar et al (2004).
This innovation would have been tremendously important. Control of fire would have allowed the migration of hominins into less temperate climes, giving them access to vastly different fauna to be hunted. Fire also extends the working hours of the day by providing heat and light, and could have allowed for additional planning or continued social bonding. Another considerable advantage of having controlled fire was protection, as wild animals rarely approach an open fire. Being able to protect one’s group as well as one’s food source would have increased home range and cut down on population loss due to predators. Since fire is portable, it may have allowed early hominins to become more adventurous as they moved around.
In addition to the Near East corridor, there is ample evidence that early Homo made the trek across North Africa and crossed the straits of Gibraltar. In Spain, the partial remains of a hominin jaw (Figure 5) and a lower premolar were found at the site of Sima del Elefante, near the town of Atapuerca.
This location will figure prominently into the discussion of the appearance of archaic Homo sapiens. These remains are clearly of hominin origin and share similarities to the remains from Dmanisi, but their fragmentary nature precludes a detailed exploration of how they relate to those at other sites. In addition to the hominin fossil remains, stone tools of a pre-Acheulean variety were found. These consist of flakes and scrapers and show little complexity beyond that found at Dmanisi (Carbonell et al., 2008). Paleomagnetism, cosmogenic nuclide dating, and the presence of distinctive fauna put the date of these remains and artifacts at between 1.1 and 1.2 million years ago.
At the site of Orce, in southern Spain, tools were discovered similar to those at Sima del Elefante and Dmanisi, but none of them were Acheulean. Following Gilbert and colleagues’ (Gibert et al., 1998) analysis of tools and other evidence, we know that humans were present in the area around 1.5 to 1.6 million years ago, but we do not know who they were.
Evidence for the earliest settlements in Italy has also been discovered in the last decade. At the site of Pirro Nord, a small collection of flakes and scrapers was found at a karst level dated between 1.3 and 1.7 million years ago by biostratigraphy and palaeomagnetism (Arzarello et al., 2007) (Figure 6). As with the Dmanisi site, from the kind and numbers of animals and plants found at the archaeological levels, the environment was open and dry. Once again, we know hominins were there, we just don’t know what they looked like.
The trek to the north of Europe appears to have taken more time, and the earliest archaeological material in Germany—an almost-intact lower jaw discovered in a sandpit—is dated between 0.7 and 0.5 million years ago. Travel to this area of Europe may have been hindered by the presence of ice. Northern Europe was often impassable during much of the Pleistocene because of glacial advances and there may simply have been no way to get there until the Donau-Günz interglacial, beginning around 700,000 years ago. That first discovery representing early Homo occurred at the site of Mauer, in Heidelberg, and is dated to approximately 500,000 years ago. When found in 1908 it was given the name Homo heidelbergensis, but it has since been reclassified as Homo erectus, a form that we will discuss in detail in the next post.
Who Were These People?
One of the frustrating things about fossil hominin studies in Europe is that we have only small amount of human remains to work with. Any reconstruction requires some guesswork based on what we uncover. But from skeletal material in the Russian Republic of Georgia, at the Dmanisi site, it is clear that these hominins had evolved beyond the basic Homo habilis form. Though we do not know exactly what they looked like, we have a wealth of evidence about their migration patterns. Hominins similar to these dwelled within Spain between three and five hundred thousand years later, and they were also found in the Near East. These discoveries come not just from limited skeletal material but also from abundant archaeological material of other kinds.
It is unfortunate that we do not have more material to work with, but the discoveries of the past thirty years have greatly advanced our understanding of pre-human history. As we shall see in the next post, the story of early Homo in Europe and the Middle East reflects only part of the hominin journey; for in addition to migrating north and west, they also traveled east.
Alperson-Afil, N. (2008). Continual fire-making by Hominins at Gesher Benot Ya‚Äòaqov, Israel. Quaternary Science Reviews, 27(17‚Äì18), 1733-1739.
Arzarello, M., Marcolini, F., Pavia, G., Pavia, M., Petronio, C., Petrucci, M., et al. (2007). Evidence of earliest human occurrence in Europe: the site of Pirro Nord (Southern Italy). Naturwissenschaften, 94(2), 107-112.
Bar-Yosef, O., & Belfer-Cohen, A. (2001). From Africa to Eurasia--early dispersals. Quaternary International, 75(1), 19-28.
Carbonell, E., Bermudez de Castro, J. M., Pares, J. M., Perez-Gonzalez, A., Cuenca-Bescos, G., Olle, A., et al. (2008). The first hominin of Europe. Nature, 452(7186), 465-469.
Gabunia, L., Vekua, A., Lordkipanidze, D., Swisher, C. C., Ferring, R., Justus, A., et al. (2000). Earliest Pleistocene Hominid Cranial Remains from Dmanisi, Republic of Georgia: Taxonomy, Geological Setting, and Age. Science, 288(5468), 1019-1025.
Gibert, J., Campillo, D., Arqués, J. M., Garcia-Olivares, E., Borja, C., & Lowenstein, J. (1998). Hominid Status of the Orce Cranial Fragment Reasserted. Journal of human evolution, 34(2), 203-217.
Goren-Inbar, N., Alperson, N., Kislev, M. E., Simchoni, O., Melamed, Y., Ben-Nun, A., et al. (2004). Evidence of Hominin Control of Fire at Gesher Benot Ya`aqov, Israel. Science, 304(5671), 725-727.
Goren-Inbar, N., Feibel, C. S., Verosub, K. L., Melamed, Y., Kislev, M. E., Tchernov, E., et al. (2000). Pleistocene Milestones on the Out-of-Africa Corridor at Gesher Benot Ya'aqov, Israel. Science, 289(5481), 944-947.
Palmqvist, P., Gröcke, D. R., Arribas, A., & Fariña, R. A. (2003). Paleoecological reconstruction of a lower Pleistocene large mammal community using biogeochemical (δ13C, δ15N, δ18O, Sr:Zn) and ecomorphological approaches. Paleobiology, 29(2), 205-229.