Lone Survivors (36 page)

In nature, it is often argued, environmental challenges force evolutionary change, and we have the saying “necessity is the mother of invention.” The price of a failure to innovate and survive is extinction, and the history of life on Earth is littered with extinctions—what can be seen as failed evolutionary experiments. However, the other side of the coin is that large, stable populations may have a greater ability to survive and to develop and maintain innovations, and I think that is actually the key to what must have been happening in Africa about 60,000 years ago. Research suggests that the optimal conditions for rapid cultural changes are those where there are large groups of interacting social “learners,” and this is the case not only in humans but in our closest living relatives, the great apes. Studies of both orangutans and chimpanzees suggest that innovations in food acquisition and processing, including the basic use of tools, happen most often not when the environment is challenging or when groups have spare time on their hands, but when large social groups are in close proximity, allowing ideas to diffuse, and useful ones to thrive. Applying that conclusion to early humans such as Neanderthals and modern humans would imply that the populations who progressed the most culturally were not necessarily the most intelligent and skillful (although those factors were important in the first place, of course), but those who were able to network and pass on learning in large groups, and to maintain those group sizes most consistently through time and space. If modern humans had the edge over the Neanderthals and other contemporary species in those respects, this may go a long way toward explaining why our species began its successful expansion in and beyond Africa, through our accelerating progress in cultural rather than physical evolution.

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.