Chris Stringer and William Davies report on two recent conferences about the Neanderthals in the 25 October issue of Nature (Stringer, C. and Davies, W 2001. Those elusive Neanderthals. Nature, v. 413, p. 791-792). Debate continues on what happened to them, and why. Assimilation by gene flow remains a possibility with a few researchers, despite the mismatch between fragmental Neanderthal DNA and that from modern people, and the inability to get Cro-Magnon genetic material is vexing. Acculturation – the influence of the behaviours of groups on one another – is also an unresolved issue. At the centre of that particular debate are tools associated with late-Neanderthal sites that bear close resemblance to those of early Cro-Magnons; the so-called Châtelperronian. The problem is precision and accuracy of dating the material, which, of course, constitute the palaeoanthroplogist’s Sword of Damocles. Dating using the decay of 14C has long been a right old mess, what with variations in the cosmogenic productivity of the isotope, and the tendency of common bone samples to pick up stratigraphically younger carbon from humic acids in soils. Charcoal is the material of choice, but in the case of Châtelperronian artefacts only associated bone seems to be available. Help might be on the way in resolving inaccuracy that stems from variable 14C productivity by using marine-core data to calibrate terrestrial 14C dates to calendar years (the “CalPal” curve). It does, however, seem to be peeking over the horizon at present.
One of the alternative processes that might have snuffed out Neanderthals is climate change. High-resolution marine records are not too useful in that regard, because they reflect global processes, and Neanderthal demise was a regional issue. Pollen records from lake sediments in Italy now reveal the intricacies of European climate during the critical period around 30 ka. It was time of rapid fluctuations in tree cover. However, similar rapid vegetation shifts occurred long before modern human influx, and the Neanderthals survived them. One possibility, allied to the competitive-disadvantage hypothesis, is that Cro-Magnons brought a steppe culture with them, which allowed them to occupy open country more successfully than Neanderthals with a woodland culture.
The topic is stymied by imprecise dating (it can be as bad as ± 4 ka), so that open-season for speculation is protracted. There is a reluctance to consider extinction through epidemic diseases brought by newcomers, and against which Neanderthals had no immunity. Disease has played such a huge role in population crashes throughout recorded history, that for it not to be at the forefront is curious. It is a widely supported hypothesis for extinction of large mammals that coincided with first entry by modern humans into the Americas ( see Late Pleistocene mass extinction – July 2001 Earth Pages). That would have had to involve jumps between species, rather than simple transmission of killers such as measles between genetically very similar populations of humans.
En route out of Africa
Finds of H. erectus and artefacts in China and Georgia date back as long ago as 1.8 Ma; the earliest signs of massive diffusion of early humans protected by their culture from entirely new climates and surroundings. The great question is, “Which way did they go?” To many palaeoanthropologists, obstacles presented by the Arabian Desert and Caucasus Mountains, favoured exit from Africa via the Straits of Bab el Mandab (closed at that time) and coastal diffusion. It now seems that movements of early humans did reach the Levant at a very early date. Ron Hagai and Shaul Levi have produced strong evidence for H. erectus’ presence in the Dead Sea rift at around the same time (Hagai, R. and Levi, S. 2001. When did hominids first leave Africa?: New high-resolution magnetostratigraphy from the Erk-el-Ahmar Formation, Israel. Geology, v. 29, p. 887-890). They found that sediments enclosing primitive, Oldowan tools (but no skeletal remains) accumulated during the period between two magnetic polarity reversals. With other evidence, these correlate with the Olduvai subchron from 1.96 to 1.78 Ma. Definitely a “first” for the Middle East, but by no means proof that this lay on the route to wider colonization, even at Dmanisi, across the Caucasus in Georgia. Little would prevent easy diffusion from East Africa along the proto-Nile or the Red Sea coast to reach the Dead Sea rift, but the obstacles to the north and east of Israel would have been far greater for poorly clad and equipped Erects.