The Improbable Primate
Page 11
The coast also offered additional resources. In 2012 we started excavating Vanguard Cave, another huge cave which is situated about 100 metres north of Gorham’s Cave. We targeted this site because it has huge archaeological and palaeontological deposits, around 17 metres thick, and because the Neanderthals lived in this cave too. We are particularly interested because earlier trials have shown that the Neanderthals at Vanguard exploited coastal resources, something which nobody had expected as it had been considered beyond their capacity. We know that at Vanguard Cave the Neanderthals consumed fish, shellfish, monk seals, and at least two species of dolphin12—and this may be the tip of the iceberg. Vanguard Cave may offer us some surprises in the future. The use of coastal resources seems to go back as far as the use of such resources by other people in South Africa.13 When we looked at the Neanderthal site of Bajondillo on the coast by Torremolinos, just 90 kilometres north-east of Gorham’s and Vanguard Caves, we found evidence that the Neanderthals there had been consuming marine molluscs around 150 thousand years ago, a date comparable to that claimed to be the earliest human exploitation of marine resources at Pinnacle Point in South Africa (Chapter 7). With a climate buffered from extremes and abundant freshwater and food resources, the coast within the south-western refuge was an important piece of Neanderthal real estate.
The importance of fresh water and marine foods in our evolution has received attention recently.14 The view that these resources were essential to our development, particularly so as to support our large brains, is probably an overstatement since alternatives to the key nutrients found in these environments are also available in non-aquatic habitats.15 Living close to fresh water and the coast would have undoubtedly permitted human populations to exploit the foods associated with these environments but that does not mean that they were incapable of surviving and doing well in their absence.
The third element of the Neanderthal survival cocktail was proximity to other Neanderthal strongholds. This would have been important because survival would have been dependent on genetic mixing of populations. Small isolated populations would have stood less chance of long-term success than those which were surrounded by others. The south-west was well placed as it had other important Neanderthal regions of Iberia adjacent to it, inland and along the coast eastwards into the Mediterranean and northwards up the Atlantic coast of Portugal and from there the Cantabrian and south-west French strongholds.
So the Neanderthals survived late in mild and humid places but what was the wider picture of Neanderthal occupation across its Eurasian range? To answer this, my research group looked at Neanderthal sites across the continent and tried to find out what habitats they had occupied in disparate parts of the range. To do this we looked at the fossil birds which had accumulated alongside the Neanderthals for clues. We found that across this vast range the Neanderthals lived close to sources of fresh water and along coasts where these were available.16 It seemed that, like the humans of southern Middle Earth, the Neanderthals were tied to water except that such sources were more readily available in Eurasia than in Africa. The oceanic west nearly always provided wet environments and the Neanderthals lived by rivers, streams, and lakes.17 Further east they would have depended more on snow melt from the high mountains, exploiting the ecological diversity provided by altitude gradients along hillsides, slopes, and valleys.18 So our earlier results now made sense. As the climates became colder and drier, the most severely affected regions would have been the continental interiors. The Neanderthals would, like the people of southern Middle Earth, have experienced water shortages and it would have been close to the Atlantic and along coasts that water sources would have remained most plentiful and where the Neanderthals would have held on for longest.
Our study of the broad, continental, ecological requirements of the Neanderthals also revealed that they had a close association with rocky habitats,19 far more than at any other point in our history and it suggests that the predisposition to visit rocky areas and shelter in caves became a part of everyday life in the cool climates of Eurasia after 450 thousand years ago just as it had for people in South Africa. It seems that it was the Neanderthals, equipped with the ability to control fire, who were the first to use caves regularly. When we turned our attention to the vegetation that composed the Neanderthal habitat we found that this typically incorporated trees and open spaces, sometimes but not always bushy thickets. Put together, the Neanderthal lineage behaved in typical Homo sapiens fashion, living in areas with trees and open spaces, and with water nearby. They lived close to the coast as well as inland. If there was a distinguishing mark of Neanderthal habitat that set it apart from many other Homo sapiens populations, it was their regular use of rocky habitats and caves. Together with their South African contemporaries, the Neanderthals were the first ‘cavemen’.
Could we find direct evidence of the impact of water shortages on the Neanderthals? We decided to go back and take another look at Gorham’s Cave.20 After the last Neanderthals, this cave seems to have been abandoned for a while. It seems that a place that had provided optimal living conditions for the Neanderthals for tens of thousands of years suddenly lost its charm. What could have happened? To try to answer this we looked for evidence in other caves around Gibraltar. We also looked at marine cores taken from the seabed for clues of climate behaviour.21 The results made us jump with excitement.
Wherever we looked in Gibraltar we found that the place had apparently become unliveable precisely when the last Neanderthals left 31.5 thousand years ago; nobody replaced them. Seismic activity was one of two key factors—we found evidence of massive falls of stalactites inside caves, rock collapses that opened up previously sealed caves, and massive landslides and rockfalls. Living inside caves or at the base of cliffs had suddenly become a hazardous business. The second factor was drought. The marine cores picked up evidence of large-scale wind-blown sand transport and of lowered river input into the sea. For a brief moment, the southwest of Iberia became a place to be avoided as three of the four key factors that suited the Neanderthals best—plentiful freshwater supplies, rocky places, and links with other populations—were lost: the oceanic influence temporarily dwindled, caves became dangerous places to visit, and there were no other Neanderthal populations left. All that remained was the coast and it is possible that the adaptability of the Neanderthals allowed them to hang on a little bit longer by exploiting marine and coastal resources when those on land had become hard to find.
Why would the Neanderthals have suffered from drought when the humans in the rest of southern Middle Earth were managing all right in similar conditions? It all has to do with the starting conditions of each lineage and their subsequent evolution in very different ecological settings.22 The Eurasian Neanderthal lineage split from the southern Middle Earth human lineage ~450 thousand years ago, at around the time when the latter had started to experience severe droughts. As we have seen, in southern Middle Earth people continued to become increasingly light and streamlined in response to the need to move about quickly over large areas, and composite tools, which improved mobility, were developed. The Neanderthal lineage also possessed this technique from a very early age, around 300 thousand years ago.23 This means that there must have been cultural transmission of information between northern and southern people after the lineage split unless we were to postulate the unlikely scenario that the same technology was independently invented by the two lineages.
The Neanderthal lineage must have experienced similar climatic conditions to other humans in places such as the Middle East—where the two overlapped sometime after 120 thousand years ago—Arabia, and possibly India. Our knowledge of the distribution of populations of Homo sapiens in these critical areas is too fragmentary for us to be able to know how far each lineage went into these regions and how much overlap there was. My hunch is that it was in the centre of Middle Earth, east of the Mediterranean and west of the high Asian mountains, that such contact must have taken place in areas where the w
arm and arid world of the south interacted with the cold and arid world of the north, perhaps in brief moments of improved rainfall.24 I shall explore this idea further in Chapter 9.
To the north the Neanderthals lived in a very different world, one of trees and open spaces, cliffs and rocky scree slopes, mountains and valleys, rivers and lakes. This covered the northern slopes of the mountains of Middle Earth—in such ranges as the Altai in Siberia, the Zagros (Iran), the Caucasus (between the Black and Caspian Seas), and the Carpathians, Alps, and Pyrenees in Europe—and it was mainly in the Far West, in Atlantic Europe, that such environments spread north and away from the mountains of Middle Earth during warm interglacials. Beyond these areas lay open, flat regions where cold deserts and steppe kept the Neanderthals out. While in southern Middle Earth humans had no choice but to continue adapting biologically and culturally to dry, open plains—they were hemmed in between harsh desert, the sea, and impenetrable jungle—the Neanderthals did have a choice, for a while at least.
Here they pursued an energetic lifestyle of ambush, hunting prey at close quarters with hafted tools in typically Homo sapiens environments of trees, open spaces, and water. Their energetic lifestyles promoted the continued development of muscular bodies and strong bones25 but their hind limb anatomy could no longer cope with efficient endurance running.26 It was the populations of southern Middle Earth that went down the new route of lightweight bodies with important consequences as we shall see in Chapter 9. The Neanderthals could afford to proceed in this muscular direction. After all, they lived in a world that did not require the far-ranging excursions of their southern cousins. It was this commitment to small-scale territories that set them back thousands of years later. Intelligent humans that they were, it seems that they tried to cope with the rapidly advancing world of treeless cold steppe when it reached them in the west but it was too late. They were overrun except in the extreme south-west where the cold steppe never reached. But their population was by then small and fragmented, and a local water shortage linked with seismic activity finished them off for ever.
9
Global Expansion of the Rain Chasers
70–21 THOUSAND YEARS AGO
According to what is called the ‘Out-of-Africa 2’ model, during the period from 70 thousand years ago, Homo sapiens sapiens spread from Africa and rapidly colonized different parts of the world, including Australia by 50 thousand years ago and Europe by 40 thousand years ago.1 However the interpretation I present here is somewhat different.
Let us take things one step at a time. What was there before and what was there after the expansion? I will not go into the timing of the geographical expansion for now at least because it would only complicate the picture. Before the spreading-out of a population of Homo sapiens across many parts of the Old World we had a lineage that occupied parts of southern Middle Earth. That lineage, which may well have had its continental variants, had become the lightly built, highly mobile rain chasers (Chapter 7). So far we have taken for granted that this lineage—the rain chasers—originated and evolved in Africa. We should not ignore the important fact that the climatic conditions that affected parts of northern and eastern Africa, and which we have seen were critical in the evolution of humans, also affected Arabia, the Middle East, and India in similar fashion. In fact, the conditions in Arabia would have been closer to north-east Africa than the latter would have been to South Africa. Yet our Africa-focused mindset seems to prevent us from comparing similar zones if they lie outside the geographical limits of the continent.2
The absence of fossils in Arabia and India has forced the ‘African viewpoint’. In any case the number of African fossils is very small and largely from the rich deposits in the north-east, particularly Ethiopia. Besides falling under similar climatic regimes, these sites are next door to the Arabian Peninsula and the Middle East and they are even closer to Iraq, Iran, and India than they are to southern South Africa. It would make sense, simply because of proximity, to expect that north-east African, Middle Eastern, Arabian, and even Indian populations interchanged genes and ideas on a regular basis, more so than they would have done with distant parts of Africa, such as the south or the Atlantic north-west (present-day Morocco). It may sound surprising but central Asia is also closer to north-east Africa than the latter is to South Africa. But the primary barrier to interchange with southern Africa would, in this case, be climate as changes in latitude would mean important shifts in temperature regimes. When conditions were favourable, during warm and wet periods, interchange between central Asia, Iran, and Iraq should have been possible. These could have been routes of cultural interchange, a way perhaps in which composite tools reached the Neanderthals and the rain chasers; from whom to whom and from where to where we just do not know.
As the northern part of Middle Earth came increasingly under the influence of the glaciations, its active part—where the cauldron of human activity was located—was reduced to the vast area occupied today by the Sahara, east to Ethiopia and the Middle East, then east again across Arabia, Iraq, and Iran to the Indian subcontinent. This was the southern Middle Earth that I have been referring to so far. Human populations would have readily exchanged genes and culture within this area which, during humid periods, would have been an Eden of lakes and rivers.3 During dry periods, human populations would have become isolated from each other in wetland refuges; if the isolation was prolonged then each population would develop its own biological and cultural identity. When populations met once more, these biological and cultural traits would have been interchanged, hence the mosaic nature of our species that was evident in Chapter 7.As this process of expansion and contraction was repeated across southern Middle Earth, genetic and cultural signals would merge or be superimposed over others. Such a pattern explains why there is so much discussion, and confusion, regarding when ‘modern humans’ left Africa, how they did it, and which routes they followed.4 There simply was no one-off Out-of-Africa; people had occupied the entire southern Middle Earth since the earliest times (Chapter 5) and different populations across this region had had contact, on and off, for the better part of 1.8 million years. The changes in the geographical range of humans did not, in this view, start with the build-up to the Last Glacial Maximum around 100 thousand years ago either, as Stewart and Stringer have suggested;5 they were not movements in the way human migrations are envisaged by many current authors6 and they did not have a specific commencement date either.
Where the flow of genes and ideas between the rain chasers and their neighbours broke down and only opened sporadically, was in south-east Asia, where rainforests were a major barrier and between Iraq, Iran, and central Asia, where cold and dry conditions would have limited the opportunities for exchange. These did happen, the genes we have acquired from Neanderthals and the Denisovans of Siberia7 bear testimony to at least two such occasions. Further west, the Mediterranean and its mountains were probably a permanent barrier, as were the Himalayas and associated mountain ranges further east. We should see southern Middle Earth as the region where a human lineage was fine-tuned into an endurance runner and long-distance walker. It was also a pump (or source region, see Chapter 6) that retained a permanent human presence throughout, albeit patchily at times, that occasionally fed areas beyond its borders. The areas beyond its borders were southern Africa, south-east Asia, and central Asia.
South-east Asia was a second pump that fed areas to the north, particularly China, when rainforests opened up and cold environments shifted northwards; during glaciations this region acted as refuge for human populations. South-east Asia may have been the original source of Homo sapiens, given the early Javan dates that are comparable in age to the earliest African ones, or it was colonized very early instead. I suspect the latter. Once established, the population remained for at least 1.7 million years, largely isolated from events in the rest of southern Middle Earth. Any subsequent contact between these populations remains obscure. We only find evidence of the rain chasers in south-ea
st Asia around 45 thousand years ago8 but the arrival of these people in uninhabited Australia between 50 and 46 thousand years ago9 indicates that they had reached south-east Asia before this time. We just do not know how many more times human populations reached south-east Asia after the first wave around 1.8 million years ago but given the many times that savannah corridors would have opened up in the area as climate cooled and became drier, it seems unlikely that we have been able to detect the only expansions that ever happened.
Let us go back to the Denisovans. They shared an ancestry with the Neanderthals and their remains have been found in Siberia, which has led to the interpretation that they somehow originated or had their core area in northern Eurasia, east of the Neanderthals. But analysis of their genetic make-up reveals that they had a lot in common with present-day Melanesians and little with Europeans and Chinese people. This has led to suggestions that their geographical range shifted southwards during cold and dry climatic pulses. What if it wasn’t like this? What if the common ancestor of Neanderthals and Denisovans lived somewhere in southern Middle Earth? From there the Neanderthal lineage could have entered central Asia and spread afterwards into Europe and the Denisovan lineage would have penetrated into southeast Asia and then northwards into Siberia, via a route east of the Himalayas.