The Improbable Primate

by Finlayson, Clive

  This hypothesis proposes that Homo sapiens selected environments that fitted into climates that fell within an intermediate range of rainfall regimes, between the hyper-humid rainforests at one end and the hyper-arid deserts at the other (Fig. 6). The closed forests would have been unsuitable because access to resources would have been very difficult and the most arid deserts would have been just as bad because of lack of water and other resources. The middle ground would have provided ample opportunities for humans to stick to their favourite formula of trees/open-spaces/water. The optimal conditions would have been provided by subhumid regimes which offered rainfall between 600 and 1,000 millimetres/year with 210 to 250 rain days/year. These regions would have offered seasonal rainfall, in some places in the summer and in others in the winter.

  FIGURE 6. The Water Optimization Model. The x-axis shows the range of humidity regimes available to humans. The y-axis shows annual rainfall (mm) with the black line showing the maximum and the grey line the minimum annual rainfall for each humidity category. The numbers above each category indicate the typical number of days of rain/year in that category. Arrow 1 represents the climatic shift of the earliest hominids around 7–6 million years ago with the double arrow indicating the range of climates tolerated; arrow 2 represents a later trend corresponding to the australopithecines; the bar numbered 3 indicates the optimal human habitat, already observable at 1.8 million years ago, with the double arrow indicating the range of tolerance; arrow 4 shows the progressive shift of humans after 1.8 million years ago towards increasingly arid climates while keeping sub-humid as optimal and amplifying their tolerance (double arrows) in the process.

  Climates at either end of sub-humid would have offered suitable places in decreasing importance the further away that we moved from the optimum. There would have been fewer opportunities in the direction of the humid end of the gradient than towards the arid end, because populations living within the humid regime31 would have soon encountered habitats, such as dense woodland and forest, which were difficult places in which to hunt and gather successfully. In other words their favourite formula of trees/open-spaces/water would have soon been lost. In the other direction, the situation would have been better as populations would have experienced a range of options, within the preferred trees/open-spaces/water combination, in semi-arid and arid climates.32 And this was the direction of physical and behavioural adaptation that, as we have seen, marked the evolution of Homo sapiens. The irony is that, in spite of their dependence on water, the climates that offered the highest amounts of rain were actually worse for humans than the drier regimes. Tethered to water but requiring areas with trees and open spaces, humans were constantly being pushed in the direction of sub-humid to arid climates which in turn provided the pressure to develop means of dealing with highly dispersed, seasonal, and ephemeral water sources. That is how Homo sapiens evolved.

  By about 200 thousand years ago, we had come a long way since the early days of the fruit-eating primate of the rainforest. What did the last stages of this evolution look like? What key features characterized the geographical distribution of Homo sapiens from around 200 thousand years ago (when people claim to observe fossils that look like us) and 10 thousand years ago (the start of present climate and the origins of agriculture)? In order to find the key attributes of these hunter-gatherer groups, I looked for the very general features that characterized the environments where Homo sapiens had lived. For this purpose, it does not matter very much, for example, if a site was close to a river or a lake; what matters is that the site was near a source of fresh water. Using the same logic, it does not matter in terms of diet if the fauna associated with a particular site had deer or antelope as both represented similarly sized packages of meat. It can matter if the different species represent different kinds of habitat but I was not looking at that aspect in this particular study. In the sense of Claude Lévi-Strauss,33 I was looking for ‘universals’, the big picture features that characterized all of our ancestors.

  To piece this together, it was necessary to trawl the literature for sites that contained good descriptions of the environments surrounding sites occupied by Homo sapiens. These had to be selected according to strict criteria. The main ones were that the site showed evidence of repeated occupation—it had a series of archaeological layers that told us that people had visited the site frequently—or evidence that the site was large and covered an important area of ground. The latter usually applied to open air sites, as caves would have been naturally confined. The reason for these selection criteria takes me back to sources and sinks (Chapter 6). A population is said to be a source population if it produces an annual surplus of individuals that emigrate from the natal population. A source should therefore be a good site if its conditions are such that it generates a population surplus. Then there are sinks. These are maintained by a supply of immigrants from source areas; a sink population is in demographic deficit because conditions are barely suitable to maintain existing individuals.

  To understand the dynamics of the population it is necessary to distinguish between sources and sinks. A human presence at an archaeological site need not represent, as is often interpreted, that the place was a good one. What if it was just kept propped up by immigrants? Such populations need to be distinguished from source ones—a tall order when looking at archaeological sites that could be tens of thousands of years old. So I chose the two criteria that I have just described as a measure of a good site worthy of a source population.34 Surely if a place was visited repeatedly or it occupied a large area—suggesting a large population—it stood a good chance of being a source? This could be wrong but it is the best we can do.

  The first observation was that the sites were not randomly distributed across the globe but were, instead, concentrated in hot spots.35 Every one of the 357 sites turned out to have been close to fresh water or the coast.36 Humans sought out sites close to fresh water wherever they were in the world. Neanderthals and the southern newcomers proved to be no different from each other in this respect. There could be no doubt that the geographical distribution of humans had been tethered to sources of fresh water and it followed that global expansion and survival in refuges had to have followed such water sources.

  Were there regional differences between sites? A southern group of sites emerged which was characterized by a mix of cave and open-air sites, a high representation of coastal sites and resources, including large marine mammals, and a high number of inland freshwater sites with large terrestrial game animals. One surprise was the similarity between south-western Iberian sites and those in Africa and Australia rather than with sites in the rest of Europe. The reason would seem to be that south-western Iberia has a highly seasonal and annually variable rainfall regime, situated within the arid to sub-humid climatic range in warm climates.37 These characteristics would have been shared for long periods across the southern flanks of Middle Earth and, during warmer, earlier periods of the Pleistocene and Pliocene, also along its northern flank.

  These climatic regimes were precisely those that would have provided optimal human living conditions. Regions with these climatic characteristics were the crucibles of human evolution: vast areas of the Sahara, the Arabian, and Indian Deserts of today38 would have been important areas within the optimal life zones of Pleistocene humans. Further east, the connection with Australia would have been sporadic depending on times when the rainforest barriers opened up during dry climatic phases.39 Once colonized by humans, biological and cultural changes in Australia would have proceeded in relative isolation. In the Late Pleistocene, south-eastern Australia, southern Africa, and south-western Iberia would have represented the extremes of this vast world. The New World was only just in the process of colonization, largely via the coasts, and so would have not yet been part of this scheme.

  A northern group of sites, representing an occupation after 45 thousand years ago, contrasted with the southern group and was dominated by open air sites over cave sites. There
were very few coastal sites but, instead, there was a high representation of inland freshwater sites with terrestrial mammals. These sites were spread across the plains of northern Eurasia and North America and were representative of the geographical expansion of Homo sapiens across northern Eurasia and into North America. These differences between regions—other regions were identified40—revealed the adaptability of Homo sapiens to different conditions. In some areas they concentrated activities on the coast and exploited its resources; in others they lived in caves and took a wide range of terrestrial animals including those that lived in the rocky habitats close by; yet in others they lived in open air sites on vast plains where large herds of terrestrial mammals were the main target. But for all this adaptability, the common denominator of all sites, the one that really dictated where to live successfully, was water.

  The Water Optimization Model predicts that the continuing adaptation of humans to an increasingly arid world permitted them to exploit semi-arid and arid areas. Here their skills at finding water were tested like never before. In Chapter 10 I will explore how they survived.

  10

  Australia

  Australia is the world’s driest inhabited continent. It offers us a unique opportunity to observe how humans took on the challenge of living in an arid world and succeeding in it. This was one of humanity’s greatest achievements and yet it is never featured as such in the histories of the world. The lack of understanding of the way in which indigenous peoples succeeded in making a living in some of the toughest environments on Earth goes back to the earliest days of colonizers and evangelists who saw backward, uncivilized peoples when they should have been in awe at the way in which these folk had managed to survive in situations in which the colonizers simply would not have stood a chance, even with their technology. Worst still, the colonizers insisted on changing the indigenous people, ruining tens of thousands of years of evolution and adaptation in a matter of decades. In Australia, the civilized colonizers were the most terrible environmental perturbation ever to have descended upon the native people of that continent. It is particularly sad and ironic that people who had lived through some of the most severe environmental challenges that any humans have ever had to endure succumbed in the end to others of their own kind who chose to see themselves as different and superior.

  The first people to arrive in Australia must have crossed a significant stretch of water, by boat or raft, at least 50 thousand years ago, if not earlier.1 These dates are in accord with the spread into south-east Asia from India after the Toba eruption (Chapter 9). They came from south-east Asia but their origin was somewhere in the core of Middle Earth. We know little else about them other than that they must have been quite used to living along the coast and that they brought the knowledge of controlling fire with them. At Niah Cave in Borneo they would use that knowledge precisely to burn down the encroaching rainforest,2 converting a closed environment into the preferred one of trees and open spaces, with fresh water close at hand in the extensive river network around the cave. These skills in adapting their environment were already with the people that reached Australia. Australia, though, was a much greater challenge.

  Not surprisingly the Australian coast seems to have attracted early settlers. Having come across the sea from similar coasts to the north or north-west, the tropical shores of northern Australia would have seemed familiar and the immigrants would have known how to live there, including how and where to find fresh water. The expansion into the interior of the continent has been the subject of much debate:3 one view proposes a rapid expansion inland, a second prefers an early spread along coasts and a gradual entry inland following the major river systems, and a third proposes an entry into the interior via well-watered regions, penetrating all areas except the arid core of the continent, which was reached much later. The discovery of human occupation of the arid Central Desert at Puritjarra, west of Alice Springs, perhaps going as far back as 35 thousand years,4 does indicate that while the early dispersal of humans in Australia probably followed coasts and major river systems, the interior was reached at a relatively early stage.5 The Out-of-Africa coastal dispersal hypothesis, by which human populations spread across the world and into Australia following the coasts, may therefore not be the whole story.6 In the case of Australia, we should remind ourselves that the people arriving there had an almost 2-million-year-old heritage of adaptation to an increasingly arid world and were well versed in the art of finding water over large distances.

  The most extreme and challenging conditions that humans would have faced would have been in the arid zone of Central Australia at the height of the last Ice Age (the Last Glacial Maximum, LGM), around 21/22 thousand years ago.7 Many locations in the region, such as the Kulpi Mara and Serpent’s Glen rock shelters, were abandoned at this time.8 These sites were situated within the freshwater riverine core of the Central Australian ranges and its well-watered hinterland. It seems that people entered these ranges at a time when there would have been more abundant resources, including large reservoirs of surface water and aquatic animals, than during the LGM. Even today they provide reliable potable water. The ranges stood out above the surrounding dune fields and sand plains and could be seen for distances of tens of kilometres.

  Not all sites within the arid zone were abandoned during the LGM. The rock shelter at Puritjarra was occupied throughout.9 This rock shelter is in a strategic position as it is located near the only permanent water source in the Cleland Hills. It is part of a sandstone escarpment and faces out onto shrubland and woodland, giving access to important resource areas as well as a range of micro-habitats along the edge of the escarpment itself. Puritjarra clearly fitted the trees/open-spaces/water specification of Homo sapiens. The archaeology at this rock shelter tells us that during the LGM, unlike at Kulpi Mara and Serpent’s Glen, small groups of highly mobile people continued to visit the site in spite of the arid conditions, though sporadically and for brief periods only. The people of Puritjarra show us that the arid desert was not abandoned altogether, a testimony to the achievement of humans as desert-dwellers. If it could be achieved in Australia, clearly it could have been achieved in the Saharan, Arabian, and Indian deserts which were fully developed by then.

  The western part of Central Australia, where Puritjarra is situated, is diverse with sand plains, dune fields, stony desert, salt lakes, and rock outcrops. Scattered across this landscape is an archipelago of small rocky ranges, each one always visible on the horizon from the previous one.10 The landscape between the hills was dominated by open vegetation, with scattered trees and shrubs, even at the height of the LGM. Provided water could be found, as in Puritjarra, humans would have been able to make a living. They seem to have been successful by having large territories and moving around them in small, highly mobile groups of perhaps 10 to 20 people. They were capable of adjusting to a wide range of circumstances within the arid zone. Their opportunistic and flexible responses to changing conditions, linked to an intimate knowledge of the terrain, allowed them to quickly focus on local resources. They could use this experience also when entering new terrain. With these skills they were able to maintain a low-density population throughout the worst conditions; low density seems to have been regulated by the distribution and spacing of permanent water, the productivity of the country which became accessible from these water sources, and the distribution and persistence of seasonal water.

  Australia offers us a completely different perspective in our quest to see how people dealt with extremely arid environments. This new window, which complements the archaeological one, is much more detailed because it gives a direct view of people living in the arid interior of Australia. Because contact between some indigenous people and western settlers happened relatively late in some places, we have first-hand accounts of how the Aboriginal people lived and survived in places too hostile for westerners. We always have to be careful in interpreting such observations especially as the influence of early contact cannot be readily
dismissed11 and we cannot fall into the trap, either, of seeing the behaviour of desert inhabitants as static and unchanging through time.12 It does not follow that the way desert people behaved a few centuries ago was exactly the same as it would have been thousands of years ago but what we are able to take home is first-hand information on how people were able to survive in such environments. That was the crowning achievement13 of almost 2 million years of evolution and the colonizers failed to recognize it as such when they came across it. It is small consolation that some enlightened people at least recorded what they saw. One such account, which I will draw from in the lines that follow, is that of Professor Robert Tonkinson,14 who met surviving groups of nomadic Mardu people in the sixties.

  How did the Mardu survive in the great Western Desert of Australia? Not surprisingly, the desert adaptation of the Mardu was dependent on living in small groups that were scattered across the landscape. The system kept a low density of population, which was the key to the sustainability of the Mardu economy. Water was at the heart of their world: the Mardu would move in response to rain, which they could detect across vast distances using visual cues, and exploit food sources, such as fish, waterbirds, and fresh plant growth, which came with it. The groups, their size changing according to local conditions and food availability, were very flexible and could move about their territory at short notice. This quick-response tactic allowed the Mardu to exploit different areas rapidly as they became available during the course of the year or even over a period of years.

  The flexible system of the Mardu, being able to adjust group size and location as the need arose, was not enough in itself to ensure survival. The Mardu had an exhaustive and very detailed knowledge of the environment and its resources and they knew well how to procure and exploit these. They were first-class naturalists; after all their lives depended on it. The amassing of the collective knowledge was transmitted to the next generation at an early stage. Children developed a breathtaking ability to read correctly the variety of signals that the surroundings produced, for example animal tracks. The long-term importance of this inbuilt database was in time-saving when out hunting or gathering, critical in times of shortage.