Based on my students’ evaluations, I spent most of last semester boring them for a few hours every Monday morning. I was running short of material toward the end of the semester, so I started throwing in lectures about topics that interested me regardless of whether they were particularly relevant. One of these is human evolution, in particular how our species (Homo sapiens) ended up at the top of the primate heap.

Anatomically modern humans (AMH) arose in eastern Africa about 160,000 years ago and,  based on their success, began to seek greener pastures about 45,000 years ago. But at the time, our ancestors weren’t the only hominids on the block. Living happily in Europe, minding their own business, were the Neanderthals (Homo neanderthalis). In a relatively short period of time after AMH arrived in Europe, the Neanderthals were gone. One of the long-standing mysteries in biology is just what happened to the Neanderthals.

For many years, the most popular hypothesis was that Neanderthals had been genetically absorbed by early humans to generate you and I. However, a number of studies comparing mitochondrial and Y chromsome DNA sequences of modern humans and DNA extracted from Neanderthal remains demonstrated pretty unequivocally that this is not the case. There is very little or no Neanderthal DNA in my genome, though the parentage of some far right pundits is still a bit dubious. One hypothesis disproven, but the question remained unanswered – what happened to the Neanderthals?

A recent paper in PLoS ONE offers some exciting new clues in the Case of the Vanishing Neanderthals. Led by American archaeologist Will Banks, a French group used a novel climactic modeling technique to answer some questions about climate in the Paleolithic and its effect on Neanderthal population. Rather than bumbling through it myself, I thought we might go and talk to the experts. Will was kind enough to take some time out to talk over their results with us:

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AFM: Let’s start with the basics. How did Neanderthals differ from early Homo sapiens anatomically?

WB: Neanderthals were more robust than modern humans. They tended to have larger chests, thicker bones, and were more developed musculature than moderns. They also had, on average, a larger cranial capacity than AMH.

AFM: What about culturally and socially? What sort of groups did the two species form? We know that humans were migratory, what about Neanderthals?

WB: Culturally and socially, it is hard to know exactly how they compared to AMH since we cannot observe social interactions. However, we do see from the archaeological record that they took care of individuals that would not have been able to provide for themselves, there are burials so we know that they cared for the dead, there is evidence for symbolic behavior, and it is clear that they were intelligent. So, it is not unreasonable to assume that they had well-developed social structures, and like modern humans, there was likely a high degree of variability concerning the nature of these social networks.

AFM: When did AMH begin to migrate out of Africa? When did the two species first begin to interact? When did Neanderthals become extinct?

WB: It appears that Neanderthals’ evolutionary separation from populations that eventually gave rise to genetically modern populations occurred around 300,000 years ago.We can recognize distinctive populations of AMH in Europe and Asia around 45-40,000 years ago.  So, the period between 50-35,000 years ago is when we see these two populations in contact in the Near East and Europe, but limitations in radiocarbon dating resolution makes it difficult to know how long this period of interaction would have been. Mellars (2006) points out that rather than being a few thousand years in length, the period of contact may have been as brief as 1,000-2,000 years, based on new high-resolution dating methods. In any case, despite some claims (which are based on problematic data and which are not viewed as being reliable by most of the archaeological community) that Neanderthals were present until ca. 28-24,000 years ago in southern Spain, the archaeological record indicates that Neanderthals finally went extinct during Greenland Interstadial 8 (39-36,000 years ago), or the subsequent GI 7, at the very latest.

AFM: I know that the idea that Neanderthals and AMH interbred to produce modern Homo sapiens has been discounted, but what type of interactions would we expect between the two? I’ve read some reports suggesting that Neanderthals may have had the ability to speak. Could there have been verbal interactions between the two species? What about trade? Would AMH have recognized Neanderthals as a separate species or at least “different”?

WB: Those are hard questions to answer since we do not have the luxury of being ethnographers for that period. I would imagine that interactions between the two populations would have run the gamut from friendly to violent interactions – remember we are dealing with two human populations over a fairly long time span. There could have been verbal interactions between the two, but I imagine it would be much like to people nowadays, who do not speak the same language, coming into contact – in other words, it would be difficult to express yourself in such a way that you are sure the other understands what you are trying to say. However, it is difficult to know how in-depth such interactions would have been. It is also possible that the two “species” avoided one another as much as possible. It is just really difficult to say anything with any degree of certainty. I think it is pretty reasonable to assume, though, that both Neanderthals and AMH would have recognized the other as being different.

AFM: Could you describe the two standing hypotheses regarding the fate of the Neanderthals?

WB: The two principal hypotheses are: 1) that climatic changes and rapid-scale climatic variability (known as Dansgaard-Oeschger variability) during Isotope Stage 3 were such that Neanderthals could not behaviorally adjust to them and over the course of time, their populations declined and they eventually became extinct; and 2) that AMH (modern humans) were more efficient at procuring resources (as hunter-gatherers) from the environments that they occupied than Neanderthals were and thus they had a competitive advantage over Neanderthals, thus eventually driving them to extinction. In our title we use the term competitive exclusion. It is important to point out that in biology and ecology, the term competitive exclusion refers to the principle that two species that exploit the same resources cannot stably coexist, and one possible result is the extinction of one of the species.

AFM: One of the aspects of your paper that I found quite interesting was the climactic modelling that your group used. Tell us a little bit, in layman’s terms, about how this modelling works.

WB: Quite simply, what the paleoclimatologists on the team did was to take a climate model, called a General Circulation Model, which describes how precipitation and temperature vary and describes climatic variability around the world, and introduced conditions that we know existed during the periods that we focused on – the interstadials (mild periods) before Heinrich Event 4, Heinrich Event 4, and Greenland Interstadial 8 – in order to simulate those prehistoric climatic conditions. For example, we know from radiocarbon-dated deep sea cores what the temperature of the ocean’s surface was during those periods, we know from ice cores what atmospheric CO2 concentrations were, we can estimate the volume of the ice sheets that were present over Scandanavia, and can estimate how much fresh water had been introduced into the oceans by the massive discharges of icebergs during Heinrich Event 4. All of these “boundary conditions” are used to “force” the general circulation model and thus simulate prehistoric climate conditions. We then refined these simulations with a very tight grid over Europe in order to achieve the high-resolution simulations (ca. 60 km grid squares).

AFM: In general terms, how do your results refute the climactic hypothesis?

WB: One of the powerful capabilities of the algorithm that we used is that one can take a reconstructed ecological niche for one time period and project it onto the environmental conditions of a subsequent period to determine where that niche would exist in the later period. When we did this for the reconstructed Heinrich Event 4 Neanderthal eco-cultural niche and projected it onto the relatively more mild conditions of Greenland Interstadial 8, we saw that the ecological conditions exploited by Neanderthals during H4 would have been present over most of Europe during GI8. However, when one looks at where we see Neanderthal sites during GI8, we see that they occupied only an extremely small geographic region of that much larger projected, potential niche. Therefore, we argue that climatic conditions did not cause their extinction. If this reduction of their territory had been climatically induced, our projections would have predicted that, but the opposite was indeed the case.

AFM: Your PLOS paper lends support to the idea that AMH simply outcompeted Neanderthals when the two species occupied the same ecological niche. Is there any evidence regarding the nature of this clash. In other words, what advantages did AMH have that allowed them to drive the Neanderthals to extinction?

WB: It is difficult to know for sure, but since modern humans were able to successfully outcompete Neanderthals for ecological resources during their period of co-existence, one could assume that there was likely some behavioural advantage or advantages.  For example, we see that their stone tool technologies were different, so perhaps AMH toolkits were more efficient at procuring resources. Maybe AMH social networks were better at allowing populations to cope with resource shortages, and perhaps these social networks allowed populations to remain more viable than what was possible with Neanderthal social networks.

9.    If you’ll indulge a bit of speculation – modern humans have demonstrated the capacity for genocide. Is there any evidence – mass graves, wounds on remains, archaeological finds – that would suggest that our ancestors demonstrated the same propensity for genocide. In other words, is there any possibility that the anatomically modern humans intentionally eliminated the Neanderthals?

No, there is no evidence of that. I think it was simply competitive exclusion in the biological/ecological sense of the term.

AFM: What’s next? Where does your research go from here?

The direction we are moving in now is to look at a single archaeological culture (called a technocomplex) and examine whether behavioural and technological variability within that technocomplex is associated with different ecological niches or suites of environmental conditions. So, rather than examining eco-cultural differences between two different archaeological cultures, we are shifting towards trying to see if it is possible to identify variability in human-environment interactions within a culture.

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Thanks to Will for taking the time to talk about his work. Will is an archaeologist by training with specialties in high-power use-wear analysis and modeling past human-environment interactions. He did his Ph.D. at the University of Kansas (rock, chalk) and then went to France to do post-doctoral work  aimed at developing the approach termed eco-cultural niche modeling with funding from the CNRS and U.S. NSF.  He is currently a research associate attached to the PACEA lab of the French CNRS and the University of Bordeaux.

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Image credits:

Reconstruction of a female Neanderthal

Human migration

European climate model

Neanderthal and human skeletons

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