Lone Survivors

by Chris Stringer

  Our closest living relatives—chimpanzees—engage in basic tool manufacture and use, in this case to crack palm oil nuts.

  We discussed the evidence for larger social group sizes in modern humans in chapters 5 and 6, along with the idea of a “release from proximity,” the ability of members of our species to interact with each other not just face-to-face at one time, as other animals do—and earlier human species did—but also at a distance in both time and space through indirect symbolic communication. One view has been that such changes are what precipitated the “Human Revolution” in Europe, with its extraordinary painted caves and continent-wide social networks, marked out by the movement of materials and innovations. But I think such changes originated in Africa, and as well as helping us survive there, such developments were the key to our ability to disperse and reach every habitable part of the world, and in doing so to displace or replace the other surviving human species. Building on some of Henrich’s ideas, the geneticists Adam Powell and Mark Thomas and the archaeologist Stephen Shennan ran computer simulations for human groups at different population densities, allowing subpopulations to develop and exchange ideas with each other or not. The model showed that subpopulation densities could reach a critical point at which ideas and skills would suddenly accumulate. Density was thus important for developing new ideas, but migration between groups was also vital, to ensure that such ideas had a better chance to persist and thrive, rather than decay and perish. Thus for the survival and propagation of knowledge, it’s not so much what you know but who you know that matters.

  Powell and his colleagues also used genetic data to suggest that population size in Africa could have reached a critical threshold about 100,000 years ago, when population density and enhanced contact between groups could have allowed the rate of accumulation of innovations to overtake their loss, something probably rare in humans up to that time. Thus cultural change in the Middle Stone Age greatly accelerated, and the increased store of learning was beneficial to the survival of individuals and their groups. In turn this would have started a feedback mechanism, leading to a further increase in population density and contacts, and so on. What is interesting about this work is that it suggests that genetic continuity, large brains, and intelligence on their own will not ensure success for human groups; the survival of knowledge itself is also vital. This may go some way toward explaining why the Neanderthals with their large brains and evident intelligence could never make the leap forward that our species eventually managed.

  They certainly made cultural breakthroughs, though—in burying their dead, producing blade tools, hafting weapons, and using pigments (predominantly darker ones than those in Africa). And, as already discussed, a recent study by João Zilhão and his colleagues of materials from two southern Spanish sites, Cueva de los Aviones and Cueva Antón, showed what they may have been doing with those pigments: they were apparently mixing colors for cosmetics to apply to their bodies or faces. Yellow, orange, red, and darker pigments were being mixed or painted in or on seashells that had been imported from the coast, some of which carried perforations (mostly natural, but carefully selected), making them suitable as pendants. But despite these behavioral innovations, within 20,000 years or so the Neanderthals as a people were extinct.

  A diagram showing limited cultural transmission in archaic humans, due to shorter life spans and smaller social networks.

  It may be that, with the constant attrition of glacial climates, followed by the arrival of modern humans, the Neanderthals were rarely, if ever, able to maintain sufficient population densities to build on their achievements. And, as we saw, the process of cumulative innovation can go into reverse, as it seems to have done in Tasmania and in Africa, even after the behavioral features of moderns started to appear. There is also another way of looking at the issue of why larger and denser populations might encourage innovation and change—and that is competition. Within human groups there has to be a continual balancing act between cooperation and competition for resources and mates. As I explain later in this chapter, the development of religion may have provided an important means of maintaining that balance.

  But as Darwin suggested, sexual selection could have been a powerful force within human as well as animal societies, an idea strongly championed by evolutionary scientists such as Helena Cronin and Geoffrey Miller. They take the view that many modern human features such as intelligence, creativity, and a way with words could have evolved not just as survival tools in the face of a hostile environment but as courtship tools, and through generations of mating preferences the genes that generated such behaviors were favored. Denser and larger human populations would also have engendered greater potential competition for resources between neighboring groups. Perhaps they managed this competition through peaceful means, such as cooperation, in trading materials and partners, or sharing religious beliefs. But otherwise, conflict over land, resources, or mates could have driven them into bouts of competitive innovation in behavior and technology, not only for gathering resources but also for weapons. As we saw from chapter 6, it could also have driven cultural and genetic changes favoring cooperative and even sacrificial behaviors within the conflicting groups.

  A diagram showing much wider cultural transmission in modern humans, due to extended life spans and much wider social networks.

  Saying that population increase was probably the critical factor in conserving and building up behavioral novelties during the Middle Stone Age of Africa still raises the question of what led to larger population densities and more extensive contacts between neighboring human groups. There are many candidates for the agent in question, one of which is climate, which, as we already saw, can dramatically affect human population numbers. I will discuss this topic in more detail later in the current chapter. We also saw in chapter 6 that modern populations have achieved both better infant survival and greater longevity compared with earlier ones, and it may be that this process was already under way in Africa before 60,000 years ago, through better technology, provisioning, and mutual support. More grandparents would have meant more intergenerational knowledge transfer, and more support for mothers with dependent children, contributing to their survival. More grandparents would also have meant more kinfolk, providing wider kinship networks across time and space, valuable for exchanges of partners and goods, for alliances, and as an insurance policy against the time that your bit of territory suffered fire, famine, or drought—in other words, spreading the risk. And perhaps something like the institution of marriage and its associated extended family structures appeared at this time, cementing social ties between neighboring groups and catalyzing the growth of ceremonies, rituals, and symbolic exchanges.

  In the same way, religion could have made a huge social impact. It was surely there, in the European Upper Paleolithic, with its depictions of what seem to be shamans and sculpted therianthropes, but I think evidence will emerge that it was also present in the later Middle Stone Age of Africa. In fact, some researchers hint that the richness of Blombos Cave may indicate that this was a sacred site, while claims have been made for the existence of a snake cult in a cave within the Tsodilo Hills of Botswana, based on a huge python-shaped rock within this Middle Stone Age site.

  Something as important as the origin and growth of religious belief certainly warrants further discussion. This is an even more controversial area than the origins of language, with most scientists accepting that religion serves social needs and is deep-seated in humans—perhaps even with an inherited tendency, like the capacity to learn language. But a minority, echoing Karl Marx’s words that “it is the opium of the people,” see religion as a pathology—a crutch that people turn to when they are under extreme stress. As we saw, once the human brain had the potential for high levels of mind reading and for episodic memory, it was ripe for these to be co-opted for religious purposes (and indeed, brain scans suggest that similar cerebral pathways are used for religious thought). As I suggested in the discussion of
episodic memory, did religion first provide a mechanism to allay possible neurosis about the future and about death, once we had the power of imagining these? Or, as Darwin believed, was it a natural consequence of human understanding of cause and effect—if there was an earthquake, or lightning struck, or the sun was eclipsed, or somebody died without an apparent cause, wouldn’t the idea of supernatural agents such as spirits and gods have automatically followed?

  Religion can certainly unite disparate and even geographically dispersed individuals to reinforce certain behaviors, and to give them a common purpose, but was the provision of emotional commitment or spiritual enforcement its original function and social benefit? Given the possibility of growing populations and more contact with other groups during the later Middle Stone Age, I think that the unifying effect of shared beliefs amid increasing social complexity would have been invaluable, providing the glue that bound people together, encouraging self-restraint and putting group needs ahead of their own. One can envisage a “successful” religion and the groups that followed it proliferating at the expense of other less successful, or nonbelieving, ones—and this competitive process continues even today. Indeed, as we saw in chapter 6, computer simulations have shown that in many situations of conflict between hunter-gatherer groups, beliefs that encourage self-sacrifice, sometimes including death on behalf of the group, can actually flourish culturally and genetically.

  There is another potential benefit of religious belief, and that is the mnemonic (from the Greek for “memory”) structures that religious myths can provide, structures that facilitate the storage and transmission of important information about the group, its history, and its environment. This is most powerfully demonstrated in the Dreaming creation myths shared by many native Australians. The Dreaming tells of the journeys of ancestral beings, animal or human, who molded the landscape and its individual features. These creator beings also passed down social rules and rituals for the maintenance of the land and the life it supports, and their journeys are marked by networks of Dreamtime tracks, joining sacred sites associated with these ancestors. One particularly widespread myth is that of the Rainbow Serpent, a huge snake that lives in the deepest waterholes, and which was born from an even larger snake marked by the Milky Way. It can manifest itself as a rainbow or can move through rivers, shaping the landscapes and singing about the places it has made. It may eat, drown, or infect those who displease it, while the righteous may be blessed with powers to heal or make rain.

  In the often hostile landscape of Australia, the transmission of Dreamtime myths through the generations must have saved many lives, since the stories provide the equivalent of an outback sat-nav, leading people to waterholes, food, shelter, and natural resources like stone and pigments. Intricate legal, kinship, and territorial systems are also built into the local variants of Dreamtime, so aborigines carry a virtual guide to life in their heads, with segments of the stories recorded in paintings or carvings, and sung or acted out at ceremonies marking the important stages of life and death.

  Dreamtime is a particularly all-encompassing creation myth, and probably took many millennia to reach its present levels of sophistication, but less elaborate versions of such stories and mnemonic systems probably existed in the Upper Paleolithic of Europe. Intricate carvings on mammoth tusks from some of the Danubian Gravettian sites we discussed in chapters 5 and 6 may well be maps of rivers and the surrounding lands, while a 14,000-year-old engraved block from Abauntz Cave in Spain was interpreted as showing mountains, rivers, and lakes, with herds of ibex. Whether that is true or not, it seems likely that symbols, ceremonies, and rituals acted like the Dreamtime stories in transmitting the oral history of Paleolithic societies and reinforcing their rules of life and their relationship to the landscape, even as far back as the Middle Stone Age of Africa. It is sad for many reasons that the surviving Khoisan (Bushman) peoples now occupy only a fraction of the range and environments that their ancestors did, to judge from the evidence of DNA, archaeology, widespread cave art, and linguistics. As we saw from the lessons of Tasmania, their decline in territories and numbers must have affected their cultural diversity, and we have thus lost the rich cosmological contexts that must have lain behind their traditions of cave art, which stretched back deep into the Later Stone Age. Similarly, the meanings of the enigmatic Bradshaw paintings in the Kimberley region of northwestern Australia are lost to us, since they represent a now-vanished artistic tradition on that continent.

  Returning to the Middle Stone Age, I want to look at the climatic record of that period, to see whether it holds clues to the growth of modern human populations and their innovative behaviors. When I was a student, the general view was that when Ice Ages hit Europe, Africa had a wet pluvial period, characterized by rises in lake levels. Similarly, when Europe enjoyed a warm interglacial, Africa suffered a dry interpluvial stage, with the spread of deserts. When I coauthored African Exodus thirty years later, in the 1990s, I proposed that a population crash in the severe global cold stage that lasted from about 130,000 to 200,000 years ago could have been the catalyst that drove the evolution of Homo sapiens in Africa. However, we now know that global climates are not read so simply, and climatic change in Africa often danced to a different rhythm from that of the major Ice Ages marked in expanding ice caps and falling sea levels.

  In fact, different parts of Africa are affected by different factors. Studies of river and lake systems and of desert dust and pollen in offshore sediment cores show that varying conditions in the North Atlantic (for example, the chilling effects of Heinrich events) clearly influenced North and West Africa. However, the East was affected by the changing patterns of the monsoons off the Indian Ocean, while South Africa was influenced by conditions in the Southern Ocean, adjoining Antarctica. At times there were windows of opportunity for humans, with well-watered conditions in parts of Ethiopia 195,000 and 160,000 years ago, at Omo Kibish and Herto respectively, but the latter period was probably much more severe in the south, with sites like Pinnacle Point providing refugia near the relative stability of coastal resources. As we saw, during the warm interglacial about 120,000 years ago, the Sahara was “greened,” with lakes and river systems, and the expansion of gallery forest and grasslands, favoring the spread of Aterian hunter-gatherers, with their distinctive tanged spear points, shell beads, and red ocher. But climatic data farther south suggest that central and southern Africa were generally more arid then, with many rivers and lakes suffering fluctuating levels, or even drying out completely. But after 75,000 years ago the situation reversed, with the Sahara turning to desert most of the time, while farther south much of Africa entered a cooler but more humid phase, with substantial rises in many of its lakes and river systems.

  Human population sizes would thus have ebbed and flowed in Africa, sometimes extensive by ancient (but not modern) standards, and potentially in contact even across the full extent of what is now the Sahara, at other times pinned back in isolated refugia like Herto and Pinnacle Point. The complex climates of Africa may also explain why there seems to be no single center of origin for the earliest signals of behavioral modernity. Perhaps North Africa (and the Middle East?) led the way 120,000 years ago, but as conditions deteriorated, populations there shrank back or even became extinct, as favored environments rapidly vanished. Perhaps the torch of modernity was then kept alive farther south at sites like Blombos and Klasies River Mouth, as conditions favored that region for a while (give or take the interruption of events like the Toba eruption). Waves of population expansion and contraction could explain the brief but extensive florescence of the Still Bay culture with its rich symbolism, and the subsequent rise and fall of the Howiesons Poort with its innovative tiny hafted blades and engraved ostrich eggshells (recently described from Diepkloof rock shelter) more than 5,000 years later. And it is my guess (though we lack much data to support it) that East Africa became one of the next centers for behavioral evolution, about 60,000 years ago, as it was from there that modern
humans (and their developing suite of modern behaviors) made their way out of Africa. My work with three geneticists on the recalibration of mtDNA evolution, discussed in the previous chapter, suggested that this was also the time of origin and first expansion of the L3 haplogroup, which gave rise to the M and N haplogroup families that characterize all of humanity outside of Africa.

  So what can we say about the factors that led to the main modern human exodus from Africa about 55,000 years ago (assuming the earlier spread to regions like Israel was only a temporary range extension from Africa)? When considering movements of humans in ancient times, we usually take into account two factors—simply expressed as push and pull. The former is caused by negative factors, forcing groups to move as a result of a lack of resources, drought, or overpopulation. The latter is caused by positive factors such as the expansion of a favored environment or the promise of rich resources, inducing movement. And some ancient dispersals were no doubt entirely accidental and without motives, for example, where a group by chance tracked game into an entirely new region, or where a boat with people on board was carried to an unintended destination by unfavorable tides or winds.