Bruce Hood - The Domesticated Brain - A Pelican Introduction (Pelican Books)

Some scientists are not so impressed with our human capacity for culture. Primatologist Frans de Waal argues that other animals also have culture because they can learn from others and transmit that learning on to the next generation. 3Famous examples of animal culture include the nut-cracking chimpanzees of Africa 4or the Japanese macaques who wash the sand off sweet potatoes given to them by researchers. 5In each case, juveniles have learned to copy what they observed in older animals. Just recently, three different neighbouring communities of chimpanzees living in the same habitat of the Ivory Coast have been shown to have distinct patterns of tool use to crack open Coula nuts. 6At the beginning of the season, when the nuts are hard, stone hammers are used by all; but later in the year when the nuts become softer and more amenable, one group switches to using wooden hammers or tree anvils. A third group makes this transition more rapidly. These distinct behaviours can only be explained by learning, as all tools are potentially available to each group.

There can be little quibble with the evidence in these examples of animal tool use, but this imitation is not the same as the cultural transmission that occurs when we teach our children. There is no solid evidence that cultural learning in animals has led to technologies that are improved upon, modified and developed from each new generation to the next. We return to this issue in later chapters when we explore how human children not only copy an adult’s tool use to solve a problem, but also faithfully copy rituals that have no objective purpose; something that animals have not been observed doing.

The debate about culture in animals is contentious, and our concern here is instead with what animal studies teach us about how humans are different. By addressing social mechanisms that most of us take for granted because they seem so natural and effortless, we examine how our brain has evolved to become domesticated, concentrating on childhood because this is when the major building blocks of domestication are laid down. But first, we must consider some of the basic processes that shaped the human brain to be capable of learning to become social.

Evolution in a nutshell

The only reasonable answer to where our brain came from is evolution by natural selection as famously described by Charles Darwin in the nineteenth century. Following from Darwin, most scientists today believe that life started out billions of years ago as simple chemical compounds in a primordial soup that somehow (we still don’t really know how) developed the ability to copy themselves. These early replicators were the precursors of life, eventually developing structures called cells. Clusters of these cells in time collected together, evolving into the ancient life forms known as bacteria that are still with us today.

Everywhere you look, from the deepest oceans to the highest mountains, from the frozen tundra to the desert furnace, or even in the volcanic acid pools that would strip the skin off most animals, you will find bacteria that have adapted to the most extreme conditions that can be found on our planet. Through the process of evolution, life forms continued to change and develop in ways that enabled them to survive different environments. But why evolve?

The answer is that there is no reason behind evolution, it just happens. Organisms evolve as adaptations to aspects of the environment that pose threats to survival and, more importantly, reproduction. When living organisms reproduce, their offspring carry copies of their genes. Genes are chemical molecules of deoxyribonucleic acid (DNA) encoded within each living cell that carry information about how to build bodies. The biologist Richard Dawkins famously likened bodies to simple vehicles for carrying genes around. 7Over time, various mutations arise spontaneously in the genes, creating slightly different bodies that lead to variations in the repertoire of adaptive fit. Some of these variations produce offspring who are better suited to the changing demands of the environment. The offspring who survive go on to produce further offspring with those inherited characteristics which worked so well, and so that adaptation becomes programmed into the genetic code that is passed on to future generations.

Through the relentless culling of those least suited for survival as natural selection dictates, the tree of life sprouted ever-increasing branches of diverging species that gradually evolved adaptations better suited to reproduce. This continuous winnowing process produced the diversity and accumulation of complex life forms that now fill the various niches of our planet – no matter how unforgiving they may be.

The ability to move our bodies purposefully around the world may have been the initial reason that brains evolved, but clearly humans are more complex than sea squirts.

Complexity suggests purpose and goals whereas evolution is a blind process driven by an automatic selection that chooses the best variations that spontaneously arise as part of the copying process. It is for this reason that Dawkins calls evolution ‘The Blind Watchmaker’. 8Any complexity that an animal has is usually sufficient to deal with the problems they need to solve. However, as environments are constantly changing, animals need to keep evolving or become extinct – which, when you look back on the course of life on earth, has happened to most. One estimate 9suggests that of all the species that have lived on the Earth since life first appeared here some 3 billion years ago, only about one in a thousand is still living today – that’s only 0.1 per cent.

There may be some controversies over the exact details and dates of this brief history of evolution, but as far as science is concerned, the origin of the species by natural selection is the only game in town when it comes to explaining the diversity and complexity of life on Earth. Whether we like it or not, we are related to all other life forms – including those with and without brains. However, human brains have enabled us, like no other animal on the planet, to bend the rules of natural selection because of our capacity to change our environment. That manipulation is largely a product of our domestication as a species.

The cost of big brains

When you consider that humans can survive in the hostile environment of outer space, where there is lethal radiation and no atmosphere, it is clear that we have considerable capacity for adaptation. When our early hominid ancestors first appeared some 4–5 million years ago, the environment was undergoing rapid changes and fluctuations that required a brain capable of versatility to deal with complex situations. 10We have brains that can think up solutions to overcome the physical limits of our bodies so that we can live under water, fly through the sky, enter outer space and even bounce around on the surface of an alien planet that has no atmosphere suitable for life. However, the processing power to solve complex problems is costly.

The modern adult human brain weighs only 1/50 of the total body weight but uses up to 1/5 of the total energy needs. The brain’s running costs are about eight to ten times as high, per unit mass, as those of the body’s muscles; and around ¾ of that energy is expended on the specialized brain cells that communicate in vast networks to generate our thoughts and behaviours, the neurons that we describe in greater detail in the next chapter. 11An individual neuron sending a signal in the brain uses as much energy as a leg muscle cell running a marathon. 12Of course, we use more energy overall when we are running, but we are not always on the move, whereas our brains never switch off. Even though the brain is metabolically greedy, it still outclasses any desktop computer both in terms of the calculations it can perform and the efficiency at which it does this. We may have built computers that can beat our top Grand Master chess players, but we are still far away from designing one that is capable of recognizing and picking up one of the chess pieces as easily as a typical three-year-old child can. Some of the skills we take for granted depend on deceptively complex calculations and mechanisms that currently baffle our engineers.