In this post, biological anthropologist James Kidder continues to tell the story of the evolution of creatures on our own small branch of the primate family tree, thehominins. In his previous post, Kidder describes the rise of the archaic Homo sapiens 600 to 700 thousand years ago. From the river valleys in Indonesia, to the open savannas in Africa, to the caves in China, India and Europe, Homo erectus had mastered fire, standardized stone tool technology and incorporated hunting into its daily life. In this next post, Kidder takes us on a tour of the transitional phase between Homo erectus and Homo sapiens.
The Genetic Evidence
In recent years, genetic studies have shed much light on the comings and goings of different groups of Homo sapiens and these studies have stretched our knowledge back beyond our own modern form and into the time of our recent ancestors.
Using pseudogenes on the X-chromosome, Garrigan and colleagues (Garrigan, Mobasher, Severson, Wilder, & Hammer, 2005) have found evidence in modern humans of ancient DNA that is Asian in origin, perhaps as old as 2 million years. This strongly suggests genetic continuity from the early Homo erectus populations through archaic Homo sapiens and to modern human groups. This lineage has its highest frequency in the southern Chinese but can be found in all of the Asian populations sampled. The authors write:
Any degree of dual ancestry in the modern human genome would either demonstrate that the transition to an anatomically modern form did not occur in an isolated, panmictic population (Cann, Stoneking, and Wilson 1987) or that replacement of preexisting hominid populations was incomplete (e.g., Brauer 1989; Smith, Falsetti, and Donnelly 1989).
The conclusions of Garrigan et al. have been contested by Blum and Jakobsson (Blum & Jakobsson, 2011), who argue that the ancient autosomal lineage patterns are consistent with an out-of-Africa scenario. However, to obtain this result, the authors were required to set their effective population size to 14,000 individuals, matching the estimates produced by the mtDNA studies. Thus, the results are only as good as the assumptions of those studies.
The general conclusions of Garrigan et al. were corroborated by Wall et al., who studied polymorphism data (Wall, Lohmueller, & Plagnol, 2009). They concluded that there is evidence for considerable mixing of ancient populations in Europe, Asia and West Africa and that this mixture represents the norm in human populations history.
The genetic link between archaics and moderns throughout Eurasia was further supported by the work of Green et al., who presented a genetic sequence of Neandertal DNA. Their results strongly suggested that Neandertals interbred with other archaic Homo sapiens populations in Eurasia and that, because of the presence of Neandertal DNA markers in modern Asian populations, there was continuity between archaic Homo sapiens and modern Homo sapiens in Europe and Asia.
This genetic evidence is in keeping with what Macintosh once referred to as “the mark of ancient Java” that he found in modern Australasian populations (Macintosh, 1965). Durband (pers. comm.) suggests, however, that, while there is good genetic evidence of some admixture, the fossil evidence suggests that some replacement (e.g. Ngandong) did occur.
Tying the Fossils and the Genes Together
One of the drawbacks of the current genetic studies is that it is difficult to relate them directly to the palaeontological evidence because beyond around 50 thousand years before the present, it is not possible to derive genetic information from the skeletal (morphological) material. Consequently, while we have clear genetic data from modern individuals that indicates admixture between archaic Homo sapiens groups, we do not know exactly how that manifested itself. If Durband is correct that the Ngandong material represent a relic population of late archaic Homo sapiens, might that also be the case for other populations in this region that are represented by some of the above crania? Based on the general paucity of evidence in this region, we simply do not know. All we can say for sure is that these crania represent an advanced condition over the Homo erectus populations that preceded them in this region. How much gene flow occurred in the process of this evolution is not clear.
The stone tool evidence in East Asia presents an unusual picture. In China, the tools that date to the end of Homo erectus time and the advent of archaic Homo sapiens are still choppers, chopping tools, cleavers and flakes. Between 100 and 50 thousand years B.P., however, several caves yield a preponderance of scrapers and flake tools and these have been favorably compared to the Mousterian of Europe, produced by Neandertals (Ofer Bar-Yosef & Wang, 2012). These tools are simple, in comparison to other areas, however and they persist for a greater period of time, stretching from west China to Siberia. It has been suggested that, as was mentioned last post, those who migrated east did not fully develop their blade tools as they did in Europe because they were able to make use of bamboo, which allowed them considerable latitude in tool manufacture, not to mention sharpness. The presence of the simple tools has been explained in that those were required to produce the bamboo tools. Bar-Yosef and Wang admit, however, that this explanation is only hypothetical at present and, as one travels north, out of the latitudinal range of bamboo, becomes increasingly difficult to support.
In Japan, despite the complete lack of late Pleistocene hominin remains, there are stone tool industries dating back to between 50 and 70 thousand years B.P. These tools are characterized as being very simple, little more than cobbles and choppers for the vast majority of the late Pleistocene in Japan (Akazawa, Oda, & Yamanaka, 1980). When they do change, they do so rapidly and there are microlithic tools found in association with bone points late in the sequence, corresponding, almost certainly, with modern human societies.
Confounding research in this area is the recent exposure of a grand hoax perpetrated by a once-renowned Japanese archaeologist, Fujimura Shinichi, who had pushed back the appearance of humans in Japan to the early Palaeolithic to between 100 and 600 thousand years B.P. Privately, it was thought that the evidence was incredible and many of us wondered (some aloud) if there was not contamination or stratigraphic intrusion. Subsequently, he was caught red-handed by a national newspaper reporter while deliberately burying stone tools at a site in order to make it look older than it was. He soon confessed to having done this at many sites, so as to enhance his reputation. It is estimated by archaeologist Shuzo Oda (pers. comm.) that as many as 90 palaeolithic sites will have to be reexamined to determine their authenticity.
Bar Yosef and Belfer-Cohen (O. Bar-Yosef & Belfer-Cohen, 2013) suggest that when the Early Würm climate in Europe became too inhospitable for the northern European Neandertals, they went south and east, bringing the Mousterian stone tool technologies with them, as is exemplified by the Middle Palaeolithic tools found at Denisova Cave, in Siberia. These authors suggest that the Levant served as a crossroads of sorts with moderns and Neandertals meeting and interbreeding. Current work by myself and a co-author, however, suggests that the inbreeding in this area is not adequately reflected in the morphology of the early modern humans there, who appear to show a morphology that is reminiscent of African archaic Homo sapiens, not Neandertals.
If the genetic evidence is corroborated, and there was population (and, perhaps, cultural) continuity across Eurasia, it could help to explain the similarity of cultural implements and skeletal morphology that is witnessed in the representatives of these populations.
What is clear from this evidence in this area and in Europe and Africa is that we, as modern humans have a concrete link to the past. No longer can we look at these remains and regard them as curios. Even if they do not completely resemble anatomically modern humans, they behave in ways that are demonstrably modern. Furthermore, we carry their legacy in our genetic code. The last great push into modernity was yet to come but the populations represented by these individuals were almost there.
Next, we will address the most alternately celebrated and reviled hominin form in the entire pantheon of human evolution: The Neandertals.