Between about 30,000 and 40,000 years ago, the Neanderthals in Europe were replaced by populations of behaviourally and biologically modern humans. What happened during that period?
The Neanderthals have had a chequered scientific career. Berated throughout the first half of the century as distinctly retarded, they were suddenly elevated in the 1960s to having been only marginally less accomplished in biological and behavioural terms than modern Homo sapiens1. But in the late 1980s they were again relegated to an extinct side-line of human evolution2,3, and this was confirmed a couple of years ago4 by the recovery of surprisingly well-preserved mitochondrial DNA from the original Neanderthal skeleton (from Neanderthal itself). European Neanderthals are thought to have diverged from the lineage that eventually gave rise to modern humans at least half a million years ago. Then, around 30,000-40,000 years ago, the Neanderthals were replaced by modern populations — probably from an ultimately African source5.
Now that the evolutionary fate of the Neanderthals has been clinched by DNA evidence, the debate concerns how this process of population replacement came about. In particular, what was the extent of contact between the final Neanderthals and the earliest modern humans6? This theme dominated a conferenceFootnote 1 held in August to commemorate the discovery of a fossil Neanderthal skull at Forbes Quarry in Gibraltar in 1848 (Fig. 1). Any process of population dispersal and replacement must involve some degree of coexistence and potential interaction between the two populations, but do we measure this in decades or millennia? Did the two groups occupy essentially the same, or sharply separated, territories? And how and why did one population, the Neanderthals, eventually dwindle to the point of extinction?
On one point, at least, there seems to be a consensus — that in the southern part of the Spanish peninsula, roughly to the south of the Ebro valley, the local Neanderthals survived for at least 5,000-10,000 years after the arrival of modern populations in the adjacent parts of northern Spain and the Mediterranean coast. A typical Neanderthal lower jaw from the site of Zafarraya in Andalusia has been dated by two separate methods (radiocarbon and uranium series) to around 30,000 years before present (BP). Equally typical ‘Mousterian’ Neanderthal technologies have been dated at sites in both southern Spain and Portugal to a similarly late period (J. Zilhao, Natl Inst. Archaeol., Lisbon; L. Raposo, Natl Mus. Archaeol., Lisbon). By contrast, characteristically modern ‘Aurignacian’ technologies, almost certainly manufactured by anatomically modern humans, have been dated at several sites in northern Spain to around 38,000-40,000 years BP.
The most likely explanation for the prolonged coexistence of these two populations lies in ecological differences between the northern and southern parts of the Iberian Peninsula. The Ebro Valley seems to act as a sharp ecological boundary for several other species, so the biological and behavioural adaptations of the expanding modern populations were probably not adequate to compete with the local Neanderthals — at least until the modern populations had time to develop their own adaptations to cope with the conditions (A. Currant, Nat. Hist. Mus., London; C. Finlayson, Gibraltar Mus.). Interestingly, despite the prolonged period of coexistence, there is no archaeological evidence that the late Neanderthal populations in southern Spain adopted any behavioural tricks or technological innovations from their new, more technologically advanced neighbours immediately to the north.
A very different pattern emerges to the north of the Pyrenees. Here, the final Neanderthal populations (as represented, for example, at Saint-Césaire in Aquitaine or at Arcy-sur-Cure in northern Burgundy) started to show remarkably similar behavioural patterns to those of the first anatomically modern populations. The Neanderthals produced simple bone tools, perforated animal teeth and other forms of personal decoration, and scattered powdered red ochre across the floors of their living areas6,7. But were these new patterns of behaviour simply copied from contemporaneous modern populations, immediately to the south, or did the Neanderthal populations in this region invent them independently, at almost exactly the same time as the modern human populations were dispersing across Europe?
Many participants at the conference found it hard to accept the hypothesis that this evolution of modern human behaviour was totally independent and coincidental. They pointed to direct dating evidence, which seems to show that the new behavioural patterns among the final Neanderthals emerged only after around 38,000 years BP — that is, only after the modern populations were already established in northern Spain (J.-J. Hublin, Musée de l'Homme, Paris; Fig. 2, overleaf). It was argued that the combination of exceptionally high Neanderthal population densities in western France (reflected in the high densities of archaeological sites in this region), together with the conditions in this area (which were cooler, with more open vegetation than in the Mediterranean areas further to the south), delayed colonization by modern human groups. In any event, evidence from both north and south of the Pyrenees shows that population replacement was by no means an overnight event, and seems to have depended on local ecological conditions, as well as on the specific behavioural adaptations of the two groups8.
The alternative picture — of an independent, coincidental evolution of typically ‘modern’ behaviour by the final Neanderthal populations, considerably before modern humans arrived in western Europe — would have dramatic implications. We would have to admit that the behavioural and cognitive capacities of the Neanderthals were every bit as advanced as those of modern humans. Not only that, but also that technological, social and cognitive ‘modernity’ could erupt at different times and places, presumably in response to some as-yet-unidentified cause. The sceptics in the audience pointed to the statistical improbability of this kind of occurrence, and to the conflicts between this picture and the rapidly accumulating dating evidence (O. Bar-Yosef, Harvard Univ.; C. Gamble, Southampton Univ.).
Aside from these debates, studies of Neanderthal skeletal remains reinforce the conclusion that they were a divergent lineage, which probably made no contribution to the evolution of anatomically modern humans. A range of anatomical features is unique to the Eurasian Neanderthals, from the detailed form of the lower jaw to the complex morphology of the inner ear. These must have evolved after the Neanderthals separated from the ancestors of modern humans (Y. Rak, Tel Aviv Univ.; M. Ponce de León, C. Zollikofer & R. Martin, Zurich- Irchel Univ.). Distinctively Neanderthal features have been identified in the 35 individuals from the Sima de los Huesos (Atapuerca) in northern Spain, at least 300,000 years BP, and in even earlier skeletons from Petralona in Greece and Arago in southern France (J.-L. Arsuaga, Complutense Univ., Madrid).
All of this is consistent with the DNA evidence that the two lineages separated at least half a million years ago4, and even longer divergence times are favoured by some workers. But how much of this divergent development can be attributed to climatic contrasts between Eurasia and Africa? Only the relatively short, stocky bodies of the Neanderthals stand out as a classically climatic adaptation, yet much of their ecological range was in relatively temperate areas of southern Eurasia, as opposed to the periglacial north. Their notoriously large noses and faces were probably due to the pressures of heavy chewing and use of the jaws as tools, rather than to any climatic adaptation to warming up cold air streams in the nasal passages. Most of the other ‘robust’ features of the Neanderthal skeleton seem to be related directly to their massive body weight, although the morphology of the upper limb bones does seem to reflect exceptionally heavy stresses in the use of the arms and hands (E. Trinkaus, Washington Univ., St Louis).
At the end of the conference we were left with the impression that the Neanderthals really were very different — well adapted to survive in the harsh glacial environments of Europe, perhaps, but with distinct anatomical and behavioural patterns from their modern human successors. Whether these contrasts reflect different mental abilities remains the 64,000 dollar question. But it could be argued that if the Neanderthals followed a separate evolutionary trajectory from the one that led to modern humans over at least half a million years, it would hardly be surprising if related divergences in cognitive capacities (such as language or intelligence) had evolved over this time9. The eagerness of some scientists to claim close kinship with the Neanderthals could come close to denying that human evolution actually took place.
*Gibraltar and the Neanderthals 1848-1948, Gibraltar Museum, 28-30 August 1998.
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