Research Achievements

January 15, 2020 

Seashells found inland in Jordan hint at why Neanderthals disappeared and modern humans survived

Long-distance resource-gathering and co-operative behaviour with distant groups may have been key to the survival of H. sapiens in the Levant 40-45,000 years ago, after the region suddenly became arid.

 

In a study recently published in the Journal of Human Evolution, a scientific team led by Nagoya University and the University of Tulsa has discovered seashells far inland in Jordan dated to 40-45,000 years before present (BP). What can evidence as flimsy as two seashells tell us? By itself, very little. But taken together with the totality of archaeological evidence we have covering a period of 150,000 years, an astounding pattern emerges that hints - just hints - at why Neanderthals disappeared and modern humans survived after the great aridification of the Levant around 45,000 years ago. The story relies on pieces of a jigsaw puzzle painstakingly gathered by thousands of scientists around the world over the last half-century, through archaeological digs in inhospitable, remote areas and careful analysis in the laboratory.

 

The prehistory of modern humans in the Levant  - a region encompassing the present-day Eastern Mediterranean and part of South-West Asia (see Figure 1) - is inextricably linked to the dispersal of our species out of Africa. This is the dominant big picture that has emerged in the last two decades, through a combination of newly-discovered physical evidence and more careful examination of existing evidence, and it completely overturns the paradigms that were widely held in the last century.  It is now known that at least 177,000 years ago, during the Middle Palaeolithic, Homo sapiens began its first phase of migration out of Africa using two routes: through the Levant - the so-called Northern Route across the land bridge linking Africa with Eurasia; and the Southern Route that passed across the Bab el Mandeb Strait at the southern end of the Red Sea and through the Arabian Peninsula: due to lower sea levels at the time, the strait would have been like a wide river.

 

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We know about the first-wave Levant route from a modern human fossil found in Misliya Cave at Mount Carmel, Israel - a left hemimaxilla (part of the upper jaw) with an almost complete set of teeth - as well as corroborating palaeogenetic and other evidence. ("Palaeogenetic" means the genetic material is actually prehistoric, in contrast, for instance, to genetic studies of living people.) Migration of anatomically modern humans out of Africa may have begun even earlier than this: a study published in July 2019 reported a 210,000 year old skull fragment discovered in Apidima Cave in southern Greece that was found to belong to a modern human. Some argue, though, that the specimen is too incomplete for its status as a Homo sapiens fossil to be certain.

 

In any case, most human migration out of Africa most likely passed through the Levant.  The Homo sapiens species eventually dispersed all over Earth.

 

The weight of evidence suggests that after the initial dispersal, anatomically modern humans occupied the Levant continuously for over 90,000 years: Homo sapiens fossils found at Skhul and Qafzeh were 90,000 to 120,000 years old. Then signs of modern human occupation peter out at about the time Neanderthals arrived from Europe at least 70,000 years ago. Nobody knows whether or not a causal relationship exists between the two events. According to decades-old speculation, the physically more powerful Neanderthals wiped out the first-wave modern human population in the Levant either directly through battles or indirectly by muscling humans out when competing for the same food resources or by introducing disease. But no direct evidence is known that conclusively supports this hypothesis.

 

The Neanderthals had migrated southward from Europe probably to avoid the increasing ice coverage in northern Europe, taking advantage of a humid and wet phase in the Levant's climate at the time. An intriguing hypothesis, backed up by some evidence, was proposed about 15 years ago by Professor John Shea, of Stony Brook University, who suggested that a short dry period prevailed in the Levant not long after the Neanderthals arrived and exacerbated the fight for food and water resources. A dry period lasting even a fraction of one lifetime can wipe out a population.

 

Overall, however, mineral deposits in caves (speleothems, meaning stalagmites and such like) show that the climate in the Levant when the Neanderthals arrived was humid and wet. This in itself is interesting because the Earth was actually in a glacial phase, known as the "Marine Isotope Stage 4", so sea levels were lower and the global climate tended to be cooler and dryer - but some local climates remained humid and wet. One of the wet regions was the Levant; another was southern Africa, where a rich archaeological record exists from that period because of the availability of water.

 

The presence of the Neanderthals in the Levant as late as 48,000 years ago has been conclusively shown by the 55,000-year-old complete adult Neanderthal skeleton found at Amud, and other Neanderthal fossils found at Dederiyeh, Kebara, Shuqbah and Tabun B. On the other hand, after a century of digging, no sign of Neanderthals has been found in Africa. Of course, absence of evidence does not prove anything; yet, since no sign of their skeletal remains has been found dated after 48,000 BP in the Levant either, at some point we need to come to terms with the likelihood that Neanderthals never made it to Africa. Why didn't they want to move further south? They certainly had enough time for it. This is an open question.

 

The second phase of modern human dispersal from Africa is generally thought to have begun as early as 65,000 years ago, which precedes the start of the Initial Upper Palaeolithic (IUP) period by 15,000 years. Stone tool and weapons technology apparently diversified in this period - the Late Middle Palaeolithic - but the subsistence behaviour of the inhabitants was similar to the preceding period in that neither modern humans nor Neanderthals carried out systematic hunting of small, quick mammals such as rabbits and birds, at least in the Levant.

 

So, in the Levant, for at least 15,000 years, modern humans coexisted with Neanderthals. (The two species also coexisted for some time in Europe, too.) The Neanderthals were physically more powerful, but did they behave differently to modern humans? Were modern humans smarter and more technologically advanced? Did they invent the new technology?

 

In fact, from the viewpoint of figuring out where the new technology came from, archaeological remains in the Levant after the second phase of migration cannot distinguish the behaviour of the two species: the stone tool (lithic) technology, although more diversified than in the "Middle Middle Palaeolithic", could have been made either by modern humans or Neanderthals. The Neanderthals could have learned from modern humans, as well as potentially vice versa, and we would have no way of knowing. The belief that modern humans were smarter and technologically superior - dubbed the "modern human superiority complex" - had been dominant for many decades until about 20 years ago, but is not widespread anymore among archaeologists.

 

In a nutshell: the lifestyle and behaviour of the two species during the Middle Palaeolithic in the Levant is difficult to distinguish in the archaeological record.

 

If we can't really tell the difference between Neanderthal and modern human behaviour in the Levant, what can we say about behaviour? There's one big surprise:  it has come to light in the last two decades or so that during the IUP, different parts of the Levant developed at different rates, culturally and technologically. Broadly, the divisions are northern versus southern, and coastal versus inland, although variations exist even within these areas, too. People in the coastal areas appear to have adopted new technological elements earlier than those living inland. Living inland apparently slowed technological progress.

 

According to one hypothesis, migration into the Levant - from the south (Africa) or east (Arabian Peninsula) and the north (Europe) came in waves, coinciding with fluctuations in climate between humid/wet and arid: wet phases encouraged migration due to more abundant food and water resources being available. Different migrations introduced different culture and technologies. Also, much of the dispersal likely happened along the coast, as it was a prominent geographical feature. Different kinds of adaptation were driven by different local microclimates, vegetation and faunal resources, and competition: the region's variety of terrains and food resources caused different adaptations driven by different local needs.

 

This is where paleoarchaeology finds itself at the start of the third decade of the new millennium. The emerging true picture is nowhere near as simple as people thought. The digging, the documentation, the analysis have to be more precise than ever. Particularly in the inland Levant, the analysis needs to be delicate because high quality fossil remains - the low-hanging fruit that make the job of inferring a history much easier - are rare there due to their being exposed to the weather for millennia: few sites are caves; most are rock shelters or in the open and so are unprotected. So we have to work harder to make sense of less clear-cut evidence, while avoiding the pitfall of extrapolating further than the evidence permits; in other words, refraining from speculation.

 

How do paleoarcheologists proceed these days? And what does prehistoric "culture" mean anyway? Helpfully, a wealth of information is contained in the remnants of stone tool industries: in the kinds of tools made and the method of manufacture (which are examples of technology); how work duties were organised in long-term occupied sites (which is an example of culture or behaviour); as well as in how the technology and behaviour can be seen to progress over millennia by examining excavated strata at decreasing depths at a single site. For example, Boker Tachtit levels 1-2 contain  tools produced using a method similar to the Levallois technique, one of the defining features of the Middle Palaeolithic (300,000 to about 50-45,000 years BP), while at the same site, the production technology progresses gradually with decreasing depth to Level 4, showing hard hammer blade production that is typical of the Initial Upper Palaeolithic, but not yet the Early Upper Palaeolithic with its characteristic "prismatic" blade and bladelet cores. Searching for these terms on the Internet brings up a wealth of images and explanations.

 

Cross-referencing culture and technologies at different strata at different sites in the Levant builds a picture of cultural development in the region during the IUP, one of cultural and technological heterogeneity where different parts of the Levant progressed at different rates, with a lag in some cases of thousands of years.

 

Then sometime between 50,000-45,000 years ago, the Levant became arid again, and stayed arid.

 

After this, no trace of the Neanderthals is known to exist in the Levant. Whether or not a causal connection with this climate event exists is uncertain, but it seems likely. The question is: why did modern humans survive the climatic aridification in the inland Levant while the Neanderthals became extinct?

 

This question was initially far from the minds of the scientific team led by Dr. Seiji Kadowaki of Nagoya University and Professor Donald O. Henry of the University of Tulsa as it set out to a dig in Jordan. Their modest goal was to obtain high-quality data in order to clarify inland Levantine IUP prehistory. Other scientists participated in the analysis, from institutions that included the University of Tokyo, University of California (Berkeley), Tohoku University, Meiji University, the Geological Survey of Japan and the Natural History Museum and Institute of Chiba, Japan.

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 The research group studied the site at Wadi Aghar, far inland in southern Jordan (indicated by a star near the bottom of Figure 1; see Figure 2), painstakingly - as modern archaeology demands - logging excavated strata centimetre by centimetre and analysing over 900 flint tools dated to between about 35-45,000 years BP (see Figure 3), and classifying their type similarity with tools found in over 40 other excavations (more precisely, assemblages) in the Levant. The strata considered at all of these sites span the Middle Palaeolithic, Initial Upper Palaeolithic and Early Upper Palaeolithic (also called "Ahmarian") periods. The Wadi Aghar assemblages are clearly distinct from those dating from the Middle Palaeolithic and the Early Upper Palaeolithic, and therefore belong to an intermediate period - the Initial Upper Palaeolithic. This makes Wadi Aghar the furthest south known IUP site in Europe and Asia.

 

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The research team had set out to do some tidy book-keeping and fact-gathering, but as so often happens in science, it serendipitously came across items whose significance appears to stand out far above the routine.

 

They found two marine shells, of the types Canarium fusiforme and (probably) Canarium cf. mutabile (Figures 4a and b). The former could only have originated from the Red Sea, at least 55km away, and was dated to 40,100-39,400 "calibrated" BP (meaning that the new, more accurate dating methodology was used); the latter, a 1cm fragment, was found about a metre away, in deposits dated to 39-45,000 years BP using a less precise dating method (they missed it because it was so small; they found it after sifting the soil from a layer, so its depth is known only to a 10cm range), and probably also originated from the Red Sea. The Canarium fusiforme certainly formed well after the Levant climate became arid, while the other shell probably did. How did the shells get there?

 

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Did Neanderthals - hypothetical descendants of survivors of the aridification - transport the shells to Wadi Aghar? Certainly, some Neanderthals, too, had been capable of long-distance procurement of resources: a few years ago, stone tools dated tens of thousands of years earlier than the Wadi Aghar shells were found in Amud Cave in Israel not far from Wadi Aghar, which were made of rock carried from a source more than 60km away. We know that these tools were made by Neanderthals because Neanderthal skeleton parts - and no modern human ones - were found with them.  Moreover, in Europe, Neanderthals are known to have transported flint and obsidian (volcanic glass) over distances of 60km or more.

 

Lead author Dr. Kadowaki has two reasons for believing that modern humans - not Neanderthals - procured the shells found at Wadi Aghar. 

 

First, the stratum at which the shells were found contained stone tools that show technological and morphological (shape) characteristics similar to others found elsewhere in the Levant that had almost certainly been made by modern humans.  The end scrapers and burins (a kind of chisel, Figure 5), and blades produced from prismatic cores, found at Wadi Aghar were most likely made by modern humans because at the other sites the same types of tool were found alongside modern human fossils. Moreover, Neanderthal bones have never been found in association with such tools. So, the logic is, either: only modern humans made these types of tool in the Levant; or Neanderthals made them (perhaps learning from modern humans) but didn't die where they made them, or they died there but their skeletons did not survive. But that's unlikely: a fair number of modern human skeletal remains have been found with such tools, and if their fossils survived, then so should Neanderthal ones. But they haven't. Therefore it's far less likely that the tools were produced by Neanderthals.

 

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Secondly, no Neanderthal fossils have been found dating after around 50-45,000 years ago, when the climate in the region became arid. The Wadi Aghar site reported in the paper is dated immediately after this event. So: the inhabitants who obtained the shells were likely modern humans who had survived the climatic aridification.

 

Indeed, excavations covering the entire period of Neanderthal presence in the Levant over 30,000 years have shown no sign of shells transported over a long distance. It is not an activity they engaged in, apparently. We have no evidence that they did.

 

Yet, in striking contrast, it is certainly true that the practice of distant shell collecting was employed by first-wave modern humans before the arrival of the Neanderthals. The oldest evidence for long-distance seashell transportation is from assemblages at Qafzeh (currently located 40km from the coast) where anatomically modern human burial sites, red ochre, and ornamental shell beads, were found, dated to the middle phase of the Middle Palaeolithic, 50,000 years before the Wadi Aghar IUP shells, and tens of thousands of years before the Neanderthals arrived!

 

Then a deafening silence sets in in the archaeological record at around the time the Neanderthals moved into the Levant and first-wave modern humans disappeared - that is, as one proceeds from the Middle Middle Palaeolithic to the Late Middle Palaeolithic.

 

Moreover, in the millennia after the owner or owners of the Wadi Aghar shells died - after about 40,000 BP onward, when the Ahmarian culture became prevalent - transporting shells became relatively commonplace in the Levant.

 

Apparently, in the Levant - according to the evidence we have - transporting shells was an activity practised by modern humans. Moreover, second-wave modern humans didn't do this until they changed their resource-gathering practice perhaps in response to the aridification of the Levant. Did they learn and adapt more quickly than the Neanderthals?

 

Procuring seashells, of course, is not the point. The Levantine Neanderthals had become accustomed to relying on local food resources only and, in addition, their population declined, probably, during the rapid adverse climate change 45-50,000 years ago. Competition for the few caves and rock shelters would have become fierce. Likewise the competition for food and water. This time (if there was a previous time) the Neanderthals' superior strength was of no use to them. In contrast, adapting quickly to the harsh new reality and changing its behaviour allowed Homo sapiens to procure what it needed from far away. The Neanderthals were doomed. And Homo sapiens, this time, survived.

 

The paper

The article, "Lithic technology, chronology, and marine shells from Wadi Aghar, southern Jordan, and Initial Upper Paleolithic behaviors in the southern inland Levant", was published in the Journal of Human Evolution in October 2019. It may be accessed at  doi.org/10.1016/j.jhevol.2019.102646

 

Authors

Seiji Kadowaki, Toru Tamura, Katsuhiro Sano, Taiji Kurozumi, Lisa A. Maher, Joe Yuichiro Wakano, Takayuki Omori, Risako Kida, Masato Hirose, Sate Massadeh, Donald O. Henry.

 

Roles and other participating universities or institutes 

The work was led by Dr. Seiji Kadowaki of Nagoya University and Professor Donald O. Henry of the University of Tulsa, with the participation of scientists from the University of Tokyo, University of California (Berkeley), Tohoku University, Meiji University, the Geological Survey of Japan and the Natural History Museum and Institute of Chiba, Japan.

 

This Media Release article was written by John Wojdylo (john.wojdylo@s.phys.nagoya-u.ac.jp). He wishes to acknowledge generous consultations with Dr. Kadowaki.

 

 

For more information, contact:

 

Researcher
Dr. Seiji Kadowaki

Email: kadowaki@num.nagoya-u.ac.jp

Nagoya University Museum, Nagoya University

 

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