technology

Wil Roebroeks and Paola Villa [1] review the evidence for human control and use of fire in the archaeology of Europe during the Middle Pleistocene (130,000-780,000 years ago) and earlier. They observe that no evidence of human-controlled fire occurs in Europe before 400,000 years ago. This raises a puzzle: How did humans occupy the northern part of Europe without fire?

The argument about the antiquity of fire is not new. There is very early evidence of fire at Swartkrans, Koobi Fora, and Chesowanja, which includes burned bones and heated artifacts, along with clay nodules that show evidence of heating as high as 400 degrees Celsius. The criticism of these early finds (reviewed by James [2]) centers around the difficulty of distinguishing human-made fire from natural bush fires. The association of the fire with artifacts can be readily explained: archaeologists only look for evidence of fire where they already have artifacts. The remaining question is whether artifacts or bones have been heated to temperatures hotter than those possible in bush fires, thereby providing evidence of human involvement. Burned bone from Swartkrans at least did reach such temperatures, seemingly unlikely without human involvement given their presence in the cave. I tend to think that humans did control fire early in some cases.

Roebroeks and Villa do not dispute possible earlier evidence of fire, but claim that it was not habitual. Or to put it another way, some early humans may have used fire, but many or most did not do so. The lack of fire seems particularly surprising in the northern latitudes of Europe, where sites like Happisburgh (and Pakefield) show evidence of human habitation in the late Lower Pleistocene. Their review of the early sites is really worth reading and impressively compact. Nonetheless, I can't quote it in full; it's just too much text to extract. After a discussion of the earliest archaeological occurrences, they turn to the long sequences from Arago and Gran Dolina, where we really should expect to see some evidence of fire if people were using it.

Arago and Gran Dolina contain long sequences and large quantities of lithic and faunal remains, subjected to taphonomic analyses (34–36). Their settings are comparable to the ones that, in later times, have often provided strong evidence of fire, such as Bau de l’Aubesier, Grotte XVI, and Lazaret in France; Bolomor Cave in Spain (Dataset S1); and Middle Paleolithic/Middle Stone age caves in Israel and in South Africa. Traces of fire have been found in the upper part of the sequence at Arago, in layers younger than 350 ka. No charcoal, no burnt bones, nor any other evidence of fire have been reported from any of the assemblages from the lower levels (dated to MIS 10–14). No charred bones or heated artifacts have been reported from the Gran Dolina sequence (TD4– TD10). Rare charcoal particles have been found in thin sections of the TD6 sediments, but these sediments originate from the exterior of the cave, and there is evidence of low-energy transport (37); thus, the charcoal may not be in situ. However, the high density of human, faunal, and lithic remains as well as their state of preservation and refitting studies (38, 39) clearly indicate an occupation in situ with little postdepositional disturbance. The absence of any heated material from the long sequences of Gran Dolina and Arago, both documenting hominin occupations over several hundred thousand years (36, 40), is striking. This is a strong pattern, which can be tested by future work at other hominin habitation sites. We suggest that the European record displays a strong signal, in the sense that, from ~400 to 300 ka ago, many proxies indicate a habitual use of fire, but from the preceding 700 ka of hominin presence in Europe, we have no evidence for fire use.

One thing that really impressed me visiting Roc de Marsal last summer was that the site preserves a long archaeological sequence in which some levels are densely packed with charcoal and the remains of hearths, and at least one well-defined layer, with abundant evidence of tools and debitage, just has hardly any evidence of fire at all. These were Neandertals, not Middle Pleistocene Homo, and they managed to get by without leaving any clear evidence of fire even though many Neandertal populations clearly did control and use fire extensively, including at this very site at other times.

There really were people living in the Pleistocene of Europe who didn't use fire very much, at least as evidenced by relatively long cultural deposits in well-stratified rock shelters and caves. Unfavorable preservation can explain the lack of charcoal or hearths at some sites, but not all of them. If we don't have a single good instance of fire in Europe before 400,000 years ago, people may well have done without it.

The authors' review of fire evidence after 400,000 years ago in Europe is also very useful, and they include supplementary data table with fuller information and references for all the sites they discuss. It is impressive just how much evidence has accumulated over the years, and Roebroeks and Villa have doggedly tracked it down. They conclude that Neandertals had essentially the same degree of control of fire as Upper Paleolithic humans, and consider the use of fire as a processing step in the manufacture of complex tools:

A recent study provides evidence of early modern humans at the site of Pinnacle Point in Southern Africa regular use of heat treatment to increase the quality and efficiency of their stone tool manufacture process 164 ka ago (13). The authors infer that the technology required a novel association between fire, its heat, and a structural change in stone with consequent flaking benefits that demanded “an elevated cognitive ability.” They also suggest that, when these early modern humans moved into Eurasia, their ability to alter and improve available raw material may have been a behavioral advantage in their encounters with the Neandertals. However, this interpretation ignores that Neandertals used fire as an engineering tool to synthesize birch bark pitch tens of thousands of years before some modern humans at Pinnacle Point decided to put their stone raw material in it. In more general terms, a greater control and more extensive use of fire is sometimes (12) seen as one of the behavioral innovations that emerged in Africa among modern humans and favored the spread of modern humans throughout the world. As stressed by Daniau et al. (52), if extensive fire use for ecosystem management were indeed a component of the modern human technical and cognitive package, one would expect to find major disturbances in the natural biomass burning variability associated with and after the colonization of Eurasia by modern humans. In their study of microcharcoal particles from two deep-sea cores off of Iberia and France, spanning the 70- to 10-ka period of biomass burning, the authors did not recover any sign that Upper Paleolithic humans made any difference: either Neandertals and modern humans did not affect the natural fire regime, or they did so in comparable ways.

I do think the silcrete processing is interesting, but so is the pitch processing. For that matter, the possibility of fire-hardening in the Schoeningen spears would be a case of deliberate production of a complex tool using fire (complex, in that the fire-processing adds a step).

Gesher Benot Ya'aqov, in Israel dating to around 800,000 years ago, is a highly compelling site in terms of evidence of fire. There are distinct hearth areas that correlate with archaeological scatter and have burned nut hulls and other foodstuffs. While Roebroeks and Villa express skepticism about the earlier evidence from Africa (specifically pointing to the high likelihood of bush fire as an explanation), they do accept Gesher Benot Ya'aqov as a likely fire location, while discussing the strength of the evidence. It's not such a high threshold to set; it seems like other sites should be able to meet it if fire was common.

Personally, I am quite ready to accept that fire was invented many times by Lower Pleistocene humans and may have occurred in some regions of the world ephemerally. The maintenance of this tradition may have been a challenge that these early humans couldn't meet over long spans of time. This view does imply that the advantages of fire, including cooking, were not a typical part of the repertoire of Early Paleolithic people. But that would be consistent with what we understand of traditions in other species of primates; where one population may be pursuing complex and apparently valuable extractive foraging that another population lacks, despite otherwise being ecologically similar.

References

Simon Armitage and colleagues [1] describe archaeological remains from Jebel Faya, in the United Arab Emirates. The assemblages come from a rock shelter in the mountain, which is around 100 km south of the Straits of Hormuz, entry to the Persian Gulf. Below Bronze Age and later remains, are three Paleolithic units. The oldest (assemblage C in the paper) is dated by OSL to the last interglacial, around 125,000 years ago. My comments here are more note-like than usual; this topic opens a window into some work we've been recently doing.

The authors' main conclusion is that the oldest assemblage displays technical similarities to East African archaeological assemblages, which are not present in the archaeology of the Levant either before or after this time. We have to dig into the supplementary material to the paper to get a good account of the technical similarities:

Technologically, this assemblage has general links to East Africa (S3 S4) while showing none of the technological traits characteristic in the contemporaneous Levantine Mousterian (S5). As in the early Middle Stone Age (MSA) of East Africa, Assemblage C exhibits three profoundly different reduction strategies: bifacial, volumetric blade, and radial Levallois. This combination is unknown in the Levant after about 200 ka, where there is no bifacial reduction and the Levallois method is largely limited to unidirectional converging. The latter produced large numbers of Levallois points, which are absent from Assemblage C.

For a layman's description of the result from coauthor Anthony Marks, I can recommend Katherine Harmon's account at Scientific American's website.

I like the observation, but I think we should be cautious about it. The basic idea is that African assemblages display three different strategies early in the reduction sequence, none of which are evident in Levantine assemblages of equivalent age.

Reduction sequences and conservatism

Yesterday I talked over this concept with my graduate student Marc Kissel. I find it very interesting that the authors focused on initial reduction stages as elements of technical similarity. They thereby assume much about the cultural transmission of the reduction sequence.

It seems reasonable that the initial steps of a reduction sequence -- from quarrying through early core shaping -- should be conservative. Early stages necessarily constrain the later steps toward finished tool production, so that a skilled toolmaker who wants to carry out the later stages of a reduction sequence has first to get the early steps right.

Paradoxically a naive learner may be ill-equipped to attend to the importance of these first steps, compared to later steps where the preform is more readily identifiable by its physical configuration. Within a social group, the early steps of reduction may well be carried out by other people, including less-skilled artificers. The best toolmaker may go to the quarry himself, but often he may call on someone less skilled to carry out the initial reduction, or may be forced to work with partially exhausted cores from earlier attempts.

I'm willing to hazard a guess that the social learning that enables tool manufacture would exert a bias toward low error rates early in the reduction sequence. We can consider a biological analogy -- early embryonic development is more strongly conserved across taxa (and phyla) than later development. Changing something early in a developmental sequence may make later events impossible. If I'm right, the argument by Armitage and colleagues should have some force -- finding that the early stages of the reduction sequence are shared among sites should be a better indicator of relationship than most archaeological indicators.

But Armitage and colleagues' conclusion has force just to the extent that we accept two proposals: (1) that we understand the technical variation in the Levant, and (2) that independent development of the early-stage reduction strategies in the Jebel Faya assemblage is unlikely.

These proposals hang together. The Levant is richly documented across the period before and after the last interglacial, moreso after OIS 6 (around 130,000 years ago) than before. These assemblages were directed toward convergent removal of Levallois points. I'm not immediately in a position to discuss the variation within these assemblages, but the question strikes me as crucial. Although the archaeological record from this area is relatively dense, like all places it samples only a small fraction of the actual groups that must have existed at the time -- to use a genetic comparison, the record has high coverage over a very small fraction of the regional behaviorome.

Was independent invention of these early-stage reduction strategies likely? The answer depends on whether a particular early-stage reduction strategy is merely rare in the large Levantine sample, or entirely absent. If such a strategy (in this case, foliate reduction) occurs at all, we can infer that its invention was possible, if not likely. With assemblage C at Jebel Faya, we are considering the cultural tradition represented by 500 artifacts. If we treated these as a random sample of the Levantine record, they are exceedingly unusual, no doubt. But random sampling across an entire record isn't the correct comparison; we want some equivalent sampling of the cultural information in terms of time and space.

The paper's conclusion that Jebel Faya represents an incursion of African-derived technical traditions into the Arabian peninsula depends on these assertions. I don't have strong feelings about them, but I think we should work to get a better statistical understanding about the issue. I am singularly unimpressed when archaeologists assert that one assemblage "resembles" another on purely typological grounds. Typological similarities may result from many constraints other than cultural information, and rare appearances actually carry a lot of information about them.

Out of Africa early

Now, what about this "southern route" business? I say it's a year behind the times. The entire reason for the "southern route" hypothesis was to explain how Africans could have left Africa 70,000 years ago without being stopped by Neandertals in the Levant. Sail them around the southern coast of Asia, and you can get them early into SE Asia and Australia without mixing with those darned Neandertals.

We obviously don't need to rule out Neandertal interbreeding anymore. We know it happened, most likely in West Asia. Putting Africans into the Levant during the last interglacial isn't a bug, it's a feature. We need contact between moderns and Neandertals in this area to explain the genetic data.

The dates may seem like more of a stumbling block. If we accept that a major out-of-Africa movement was underway by 70,000 years ago, we are going to have a hard time explaining why the Levant seems to have been entirely uninfluenced by it.

But a 70,000-year-long chronology, based on estimates of mtDNA haplogroup divergences, is already out of kilter with the majority of evidence. Nuclear DNA suggests a substantially longer timescale, which would derive non-African and sub-Saharan populations from common ancestors before 140,000 years ago. Depending on the amount of mixture among these populations and the mutation rate we adopt, these populations may have begun to differentiate very early in the Middle Stone Age.

It's hard to account for the diversity of people outside of Africa with a short migration timescale. People outside Africa are around 20 percent more inbred than sub-Saharan Africans, but they don't look like they underwent any sudden severe bottleneck. Even accounting for the mixture with archaic people like Neandertals and Denisovans, much of the variation of Middle Pleistocene humans (still present in Africa) just didn't get into non-Africans.

I would propose a movement of MSA Africans into West Asia before the last interglacial as a model that provides a good fit to these data. An early movement followed by long interactions in this limited area would explain so much of the population structure and morphological variation of MSA Africans wasn't represented in the people who peopled Eurasia. A substantial delay between the initial entrance into West Asia and the dispersal to Europe and the rest of Asia would explain why the later archaeological transitions in those regions have no sign of immediate technical or cultural links to the MSA. It would also explain why the initial "modern" humans outside Africa share few if any derived morphological features with Africans after 100,000 years ago.

The anatomy of the Skhul and Qafzeh samples suggests that an African incursion into the Near East did occur before 100,000 years ago. Many paleoanthropologists have supposed that this early incursion did not persist, even locally. The later Levantine sample includes individuals with more Neandertal resemblances, chiefly Amud and Kebara. But each of the later specimens shares several traits with early modern humans from Skhul or Qafzeh. Indeed there is no clear constellation of derived traits that sorts the Skhul-Qafzeh sample cleanly from Tabun 1 and the later Levantine specimens. I just don't think this skeletal record poses any problem for the idea of a long interaction of populations in this area -- especially if we extend the focus from the Levant into the Arabian peninsula and Persian Gulf region.

The strongest reason to suppose that an African incursion was extinguished is not the skeletal record but instead the mtDNA timescale. I can refer readers to the paper by Endicott and colleagues [2], which discusses a range of mutation rate estimates and their effects on the origin of macrohaplogroups M and N, the key ancestral non-African lineages. Current estimates unanimously suggest that these clades originated within the last 75,000 years. By itself, this would suggest that the mtDNA common ancestors of non-Africans and sub-Saharan African populations diverged shortly before that time.

I keep coming back to this, because the mtDNA just seems so out of line with the autosomal and X-chromosome picture. I regard this as a serious sticking point and hesitate to just wave it away. As I suggested to Charles Choi, the resolution may involve a time of isolation outside Africa during which the ancestors of non-Africans lost heterozygosity (and became enriched for the later mtDNA clades M and N). Or maybe we just have the mtDNA clock wrong -- the large revisions of the Neandertal-human mtDNA divergence in the light of developing evidence don't inspire confidence about the timing of internal nodes to the human mtDNA tree.

The early archaeological assemblage from Jebel Faya strikes me as consistent with a model of early dispersal from Africa, but not especially good evidence for it. The outstanding question is whether the early reduction strategy is a behavioral trait that provides good evidence about biological relationships. I see the logic but think that it is tenuous.

The model obviously is relevant to the question of an early presence of African-derived modern humans in India. If we combine the presence of an African-derived population in eastern Arabia with the large exposed Persian Gulf region during the last interglacial, this begins to look like a large habitable region with easy land connections to the Indus River valley. But the Indian subcontinent would potentially have been home to a very large population of ancient humans. I doubt that an occupation across the large area of West Asia plus the Indian subcontinent would have enabled the substantial reduction of heterozygosity that we see in present-day non-Africans.

References