The twilight of the neanderthal

Author: Alvaro Arrizabalaga received a BA in History (Vitoria, 1988) and a Master in CRM -Archaeology option- (Vitoria, 1992) at the University of the Basque Country (Spain). He finished his PhD in Prehistory (La industria lítica del Paleolítico superior inicial en el oriente cantábrico) in 1995. He has been a lecturer of Prehistory in the University of the Basque Country since 1995. His archaeological fieldwork has focused on the excavation of Palaeolithic sites, such as Labeko Koba, Lezetxiki or Irikaitz, in the Iberian Basque Country. His research related publications include several articles and contributions to different scientific meetings. His main interests are human cultural and symbolic behaviour at the Middle to Upper Palaeolithic Transition.

All aspects of the replacement of Neanderthals by our own species are the subject of controversy in the scientific community and even transcend to the mass media and civil society itself. For the archaeologists working in this topic, it is sometimes hard to explain with all appropriate nuances why we need to modulate our opinions and occasionally, based on limited analytical foundations, reach conclusions that are contradictory with what was expressed only a short time previously. Prehistoric archaeology, despite being a very young discipline (barely a century and a half old), is built upon analytical procedures that bring together very different kinds of specialists (biologists, anthropologists, geologists, physicists and chemists, among others), as well as the archaeologists themselves, which to a certain extent explains why it has advanced in a kind of “stop/start” process in our handbooks. The appearance of a new analytical procedure, innovative approach or a site with unusual characteristics tends to force us to take some steps backwards, in order to re-take the path of a consistent discourse. Thus, for example, the first results of the genetic sequencing of Neanderthals appeared to rule out, until 2009, the possibility of hybridisation between Cro-Magnons and Neanderthals. However, since then such hybridisation has been regarded as real and measurable because, in that year, certain genetic traits of Neanderthals were first detected in individuals of our species.

More recently, our ideas about the circumstances of the twilight of the species that preceded us in human evolution have taken another dramatic turn. Since the late 1980s, it has been assumed that the last Neanderthals withdrew from Northern Europe to take refuge in the southern peninsulas (Iberia, Italy, the Balkans and Crimea). A large number of dates from younger sites in these refuge areas seemed to indicate that they had survived there (due to ecological, subsistence or demographic conditions, it was speculated) for many millennia. The arrival from the Near East of the first modern humans (Cro-Magnons or Anatomically Modern Humans) in these peninsulas would have been witnessed by the Neanderthals, who co-existed with the newcomers over a long period (up to 10,000 years was proposed for the Iberian Peninsula). This scenario, which was plausible with the data available until 2010, opened large windows for interaction between both species, both from the biological point of view (hybridisation) and from technological, cultural and behavioural perspectives. Directly or indirectly, the activity of our species was given – at that time – as the most likely cause for the extinction of the Neanderthals.

We have already noted the first nuance to be considered in the disappearance of the Neanderthals, as a large part of modern humankind carries in its gene pool a small percentage (less than 5%) of genes that come from the Neanderthals. Therefore, we know that the two species hybridised, which ought to support the hypothesis of a long co-existence of the species in the southern peninsulas of Europe. However, to judge from the weight these genes still have in the Euroasian pool, the geographical distribution of these traits and other data, the hybridisation must have taken place outside Europe, most probably in the Near East, where the two species lived together for up to 50,000 years. When modern humans entered Europe, about 44,000 years ago, they already possessed a small Neanderthal component in their genetic line. Those windows of opportunity for interaction and cultural exchange in southern Europe still remained, but even this hypothesis was to be rejected in the light of new dates obtained in various regions.

The reason for this new approach is connected with analytical refinement in radiocarbon dating techniques. ¹⁴C, which in itself is very rare (only one atom in a trillion carbon atoms correspond to this isotope), begins to disintegrate when the prey that has been hunted dies or when the branch used for firewood falls from the tree. At a constant and relatively fast speed (half of them every 5700 years, approximately), the atoms disappear, so that after the sixth or seventh stage of half-disintegration, the portion left in the bone or charcoal is so small that the slightest contamination alters the result of the analysis dramatically, and may reduce the age significantly. In the last ten years, different radiocarbon laboratories have developed ways to treat the samples, before measurements are taken, to ensure that all the contamination that occurred after the deposition of the sample is removed, and the reliability of the results is optimal.

However, the application of this pre-treatment to samples from levels left by the last Neanderthals and the first Cro-Magnons in Western Europe is producing very different results from what was expected¹. In the first place, some sites which were believed to be well-dated have been shown to be more contaminated than was thought, and in many cases the conservation of the materials does not allow (and did not allow when the first determinations were made) reliable dating. Secondly, those sites with suitable conservation conditions to guarantee accurate dates have provided results thousands of millennia older than expected just a few decades ago. Finally, the superimposition of dates for the last Neanderthals and the first Cro-Magnons in the same regions do not seem to correspond to reality, or to put it another way, there does not seem to have been a time when the two species co-existed (or at least, not a prolonged time) in any part of Western Europe, including the southern peninsulas². For the Iberian Peninsula, the publication of a series of papers dating or re-dating levels corresponding to the last Neanderthals (even those in the far south) appears to set back their disappearance to about 45,000 or 44,000 BC, whereas the first presence of our species at northern sites (Labeko Koba, in the Basque Country; L’Arbreda in Catalonia; and La Viña, in Asturias, recently published³) is dated about a millennium later.

Obviously, the value of this information is relative, if we take into account the margin of error in the radiocarbon dates and overlapping between the probability curves, in order to deliberately search for a scenario in which individuals of the two species met in person. It is possible that this happened and given the uncertainties that affect our discipline, it cannot be ruled out for Iberia or any other area with coherent results (Great Britain, France, Germany and Italy). However, reducing the size of the window of opportunity mentioned above, from ten millennia to a few centuries at most, greatly minimises the possibilities of interaction between the species. Not only in the biological aspect (which is less important, because it is already established that the Cro-Magnons who arrived were hybridised), but above all, in the field of technology, culture and symbolic behaviour. And additionally, it should be said, it reduces the likelihood that the activity of our species in some way influenced the disappearance of the Neanderthals, our cousins on the phyletic scale.