Ignacio de la Torre

The transition from the Oldowan to the Acheulean: Where do we stand?

When and how the Oldowan was replaced by the Acheulean are key questions in the archaeology of human evolution, and will be discussed in the context of biological and ecological change in East Africa.

FULL TRANSCRIPT 

Good afternoon. First of all, I would like to thank the organizers of this conference for inviting me to contribute. I really feel privileged to participate in distribute to Dr. Richard Leakey who in one way or another is associated with many of the sitesI will be talking about today. The Acheulean is a major event in the evolution of human technology and marks a significant change from its predecessor of the Oldowan. This is likely related to a speciation episode that leading to the emergence of Homo ergaster from an ancestral form of early Homo. And in this talk I'll discuss this transition from the point of view of the archeology and focus on what we currently know and what we would like to know on the origins of the Acheulian and the demise of the Oldowan. But first a little a bit on what we mean by each of these technologies. 

In a nutshell the Oldowan complex is characterized by a core and flake technology which is dated between 2.6 and 1.6 million years ago, and which was first discovered by Richard's father Louis Leakey at Olduvai Gorge. On the other hand, the Acheulean is often identified as such by the presence of a particular tool, the hand axe. The earliest Acheulean is currently dated to over 1.7 million years ago, whereas the latest typical Acheulean hand axes are still present, 1.5 million years later making all this technology the longest lasting in the history of humankind. Hand axe production is substantially more complex than Oldowan flaking, both in terms of technical skills and cognitive operations involved. It requires the imposition of a specific mental templates and in entails a hierarchical organization of flaking actions. In addition, this planning also requires flexibility and adaptability to the particularities of each piece of raw material. This alongside the craftmanship required to do the job involve a technical and cognitive leap from the Oldowan into the Acheulean. 

Okay, now that we've reviewed briefly the technological grounds, I'll move on to presenting the chrono-stratigraphy of the first Acheulean. This graph shows radiometric ages for the earliest Acheulean in East Africa. Now all the sites that might be in the same chrono-stratigraphic interval, but I haven't included them here due to a lack of reliable dates. In contrast for west Turkana, for Konso, Gona and Peninj, tuffs and paleomagnetism have provided relatively consistent ages. So according to currently available data, the oldest hand axes are those from West Turkana and Konso. In West Turkana the earliest Acheulean as Sonia was saying this morning is reported at Kokiselei 4 with an age of about 1.74- 1.76 million years ago and nearly identical is the age for early hand axes in Konso in southern Ethiopia. Here the earliest site is well dated to around again 1.75- 1.74 million years ago. 

Interestingly, whereas in west Turkana there seems to be as far as I know, very few sites with hand axes. After Kokiselei 4 and in Konso, a number of early Acheulean assemblages are found through the sequence. And this makes of Konso a useful comparative sequence to frame the other Acheulean sites which are all younger than west Turkana and Konso. In the case of Gona, early Acheulean assemblages are starting now to be polished and some tuffs capping Acheulean materials are earlier than 1.2 million years ago. So, it is estimated that the older Acheulean sites are substantially earlier than that 1.2-million-year-old date. Indeed, an age of between 1.6 to 1.5 million years ago is given to Dan5, which contains early hand axex associated to Homo erectus remains. It is also relevant because to my knowledge is one of the few assemblages where we have a direct contextual association between very early hand axes and Home erectus fossils. Well, thanks to the long history of research at Olduvai in Tanzania, there is there a solid chrono-stratigraphic sequence, and the appearance of hand axes is well-documented from the middle part of Bed 2 right above the green line drawn in this slide. Tuff 2D at the top of Bed 2 is dated to around 1.3 million years ago, whereas tuff 2A is 1.7 million years ago. So, an age of around 1.6 million years is estimated for the earliest hand axes at Olduvai. 

I'm very close to Olduvai and also in Tanzania, Peninj in the west of Lake Natron. Peninj is famous for the Australopithecus boisei mandible that Bernard was talking about before yesterday, but it also has an important early Acheulean sequence discovered by Glen Isaac and Richard Leakey. This archeological sequence is close to Olduvai, not only geographically but also chronologically. Mugulud and Bayasi sites are capped by a tuff dated to 1.33 million years ago. So, an age of around 1.4 million is proposed for these early Acheulean sites. So, to summarize, there is good evidence that the earliest hand axes appeared at least 1.75- 1.76 million years ago. And then a number of sites indicate that this technology was well established in East Africa by 1.5 million years. So, the earliest Acheulean is located in the north of the Rift Valley with west Turkana and Konsa and slightly later Gona. The next well dated early Acheulean sites are those of northern Tanzania with Olduvai Gorge and Peninj and by around 1.4 million years the Acheulean is also found beyond East Africa with hand axes in South Africa and also out of the continent suggesting quite fast dispersal for this technology. 

Okay, once we've reviewed the age of the early Acheulean, let's have a look at the archeological assemblages. With regards to the paleoecology, the truth is that we still don't know much. Regional settings for early Acheulean assemblages are basically the same as in the Oldowan. Broadly speaking, yes, early Acheulean sites are often in more open environments than during the Oldowan. However, it is not clear whether this is a specific feature of the Acheulean or just a product of the overall climatic trends towards rare conditions. Actually, both in Kokiselei 4 in Turkana and KJA6 in Konso remember these earliest Acheulean sites, palaeoecological proxies indicate a closed habitat rather than the open grasslands typical of most of the fossils record of 1.6 million years ago. Therefore, I think we should be cautious when making direct associations between the emergence of the Acheulean as a technology and adaptations to more open environments than during the Oldowan. 

Anyway, let me say again that we still have very little data on the paleoecology of the earlier Acheulean, and this is definitely a topic that requires much more research in the future. The same applies to subsistence strategies. While the hunting versus scavenging debate during the Oldowan is 40 years on still rather contentious today, we know much less about the subsistence of early Acheulean tool makers. New research is providing solid associations between stone tools and animal fossils. However, I think we are still unable to address properly how different subsistence strategies were in the early Acheulean when compared to the Oldowan and the extent to which hand ax tool makers had primary access to carcasses. Contextual problems don't help to address such questions because as you may notice in this table, fossils are poorly preserved in a number of early Acheulean sites. However, bones are present in some more recently excavated assemblages. 

So, we start to see some patterns emerging and a few differences in subsistence strategies are observed between the late Oldowan and the early Acheulean. HWK EE for instance is a site discovered by Mary Leakey at Olduvai but never published and which subsequently we have excavated for a number of years. Dated to 1.7 billion years ago, it is one of the last Oldowan assemblages before we start finding hand axes in the Olduvai sequence. And here at HWK EE, abundant cut marks show that there is clear human manipulation of mammal bones but, there is also strong carnivore signature in the assemblage just as is the case for most of earlier Oldowan sites. And we have some evidence that allows us even to figure out who got it first. As we can see in this Bovid bone, which I put here as an example, tooth scores indicate early access by carnivores to the carcass and such tooth scores are offset by cut marks that indicate hominin scavenge the carcass from the carnivore. Having said that, seems as if late Oldowan hominins had it their way sometimes as this cut marked hyenas scapula seems to suggest. 

In early Acheulean sites, however the story seems to be different and hominin/carnivore competition is less obvious, whereas the human signature is much stronger suggesting that hominis are the prime agents in the formation of assemblages, which often involve very, very large mammals with clear evidence of human manipulation. But let's move on to what the stone tools say. Comparatively we know much more about technological differences between the as Acheulean and the Oldowan than about their subsistence behaviors. In Kokiselei 4, hand axes are predominantly made on cobbles and these hand axes are really big and massive with several of them over 20 cm in length. The oldest Acheulean in Konso is dominated by picks, cleavers and all the large cutting tools and are often made on a very large basalt flake as well. And interesting feature of the early Acheulean in Konso is the presence of shaped bones, which include large cutting tools like those made in volcanic rocks. Interestingly, bone shaping is also documented in the early Acheulean of Olduvai Gorge suggesting that specific mental templates are imposed regardless of the raw material, be it a bone, be it a rock. And coming back to the lithics, the early Acheulean hand axes from Olduvai and Peninj are good examples of the technological patterns emerging with the Acheulean after the Oldowan. 

Starting with Olduvai, we can use the case study of EF-HR excavated by Mary Leakey first and then recently by us, whereas where a large number of early Acheulean artifacts are preserved. Most of the EF-HR hand axes are not really bifaces but universally retouched large flakes. This shaping is normally over the dorsal face whereas ventral sides remain largely unmodified. Yes, there is some bifacial retouch but it mostly involves shaping of tips only where there is no thinning of the volume nor is there an attempt to get symmetrical plan forms. In general, most of these LCTs are just what we call massive side scrappers where denticulate retouching of one age is associated to shaping of convergent tips and where classic features of a bifacial flaking are essentially they're absent. 

Most of the time we don't find the LCT the large cutting tool cores. So, there is a clear fragmentation of the reduction sequence with hand axe blanks produced elsewhere and then transported to the sites where we are finding them. The early Acheulean in Peninj is nearly a replica of what I've just described for Olduvai Gorge. In Peninj, hand axes are made mostly on flakes from very large cores which involve preparation of massive, of massive boulders. Like at Olduvai, large cutting tools from Peninj are mostly unifacial with only a few pieces that are shaped bifacially and again, like Olduvai, these hand axes are just huge side scrapers rather than proper bifaces. And the main goal again is to produce strong tips while the rest of the artifacts are very poorly shaped and like in Olduvai the reduction sequences fragmented with LCT blanks, produced elsewhere and then transported to the sites. This fragmentation of the reduction sequences during the earlier Acheulean seems to be not exclusive from Olduvai and Peninj. We can observe it also in several other sequences in the Koobi Fora affirmation for example, firsthand axes are roughly around 1.4 million years old, more, or less the same age as Peninj and located at different distances from raw material sources. Hand ax variability across the Koobi Fora sites is interpreted as representing a single lithic economy strategy integrated within a patent used of the landscape.

In short, in all these hand ax burying sites, we document a clear temporal and geographic break or flaking activities which we think must be related to more complex foraging strategies in the Acheulian when compared to the previous period to the Oldowan. This takes me to the next point that I like to discuss, which is the actual evidence for the transition to the Acheulian. Well the classic hypothesis of the so called developed Oldowan based on the Olduvai sequence interpreted stone tool variability from middle Bed 2 as the result of different cultural traditions made by biologically distinct hominins. As it was proposed that the Acheulean was made by Homo ergaster and then developed Oldowan by Homo habilis as a response to this new technology brought by Homo erectus, the Acheulean. Well, this hypothesis has been a subject of a debate over the last few decades with authors in favor or against the existence of a developed Oldowan once the Acheulean appears in the archeological record. Our early reviews of the Olduvai sites tended to downplay inter-assemblages differences that are supposed to separate the developed Oldowan from the Acheulean, for example, size disparities between developed Oldowan and Acheulean hand axes we believe that can be explained by typological misclassifications in many instances and we showed that real hand axes from all sites are actually sharing similar dimensions, be it Acheulean or so-called developed Oldowan. 

The ability to produce large flake blanks, which is indeed defining future of the early Acheulean also exists in the assemblages, initially classified as the developed Oldowan and the alleged poor shaping of hand axes in the developed Oldowan can also be challenged. As I mentioned before, earlier Acheulean hand axes are very often simple unifacial large cutting tools while in assemblages originally considered as developed Oldowan, some well flaked true bifaces are indeed present. In short, we've argued that in the case of Olduvai, once hand axes appear in the sequence, all assemblages should be considered as Acheulean, and a stone tool variability is a consequence of multiple functional and ecological factors. We have proposed something similar for Lake Natron. Here, ecological localities are geographically apart with some sites in the Delta and others in the middle and upper course of the Peninj River. Since these geographically distant sites are within the same stratigraphic interval, we interpret technological differences between them as evidence of technological variability across the Acheulean landscape and an adaptation to the functional needs and paleoenvironmental settings of each locality. So yes, the ecological hypothesis may explain in part the technological variability observed in earlier Acheulean times with different toolkits according to distinct paleoenvironments. 

But I just said the ecological hypothesis explains it in part only and that's because the binomial Homo habilis equals Oldowan and Homo ergaster equals Acheulean still seems to work in some places such as Olduvai. Here, not a single Homo habilis fossil has so far been reported in hand ax bearing sediments. For instance, we have recently re-excavated the MNK skull site, yet another site discovered by Mary Leakey, which has the last appearance of Homo Habilis in Olduvai. The site is in the same position as HWK EE side I mentioned earlier when talking about carnival human competition and it's very close stratigraphically to the earliest hand axes in the sequence of both. When we started excavating there, we hoped that we could track changes in the technology signaling the advent of the Acheulean, which we know is only a few meters higher in the stratigraphy. No hints were found though. The site is solid Oldowan, and its score and flake technology doesn't look very different at all from sites half a million year older. The main case will be around 1.6 million years old, a time period when we know that the Acheulean was already in place further north in the Rift valley. 

And this brings us to another riddle. These days is fairly unpopular to attribute technological variability to separate cultural groups. But how do we explain such technological variability when biological diversity is indeed demonstrated well given the long temporal overlapping that we know existed between Homo ergaster and Homo habilis? Well, it's not totally out of the question to propose that technological variability can be at least in some cases explained by biological differences. I dare not to dwell too much on the Turkana sequence even that most of the people here today know it by heart and I definitely don't. But the possibility that stratigraphic overlapping of Homo ergaster and Homo habilis may exist has relevant implications for interpreting stone tool variability in the region. We have another paradox despite the traditional association of Homo ergaster and the Acheulean, and even though in Koobi Fora we have the earliest Homo ergaster and continued presence of this species throughout the record. Well, we are yet to hear about very early Acheulean in East Turkana, which gets even more interesting when we bear in mind that on the side of the lake, we actually have the oldest as Acheulean hand axes. In summary, there is a complex archeological and paleontological record in the time span of the Oldowan Acheulean and a convoluted set of possibilities to explain archeological variability and its correlation with biological diversity in the genus Homo. 

So it looks like the same. All questions formulated decades ago are still present. We still know little about adaptations of the last Oldowan tool makers mechanisms that gave place to the emergence of the as Acheulean are still poorly known and we really need to interpret archeological assemblages in the life of the biological diversity observed in the timeframe of the Oldowan-Acheulean transition. All of this makes of current research on the transition to the Acheulean vibrant field on which research in the Turkana Basin in for sure must play a most important role. That's it. Thank you for your attention.

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