Wired for Culture: Origins of the Human Social Mind (34 page)

But even in this arms race neither herbivore nor carnivore brain sizes come close to those of primates, much less our own. This might be because the arms race between herbivores and carnivores is still somewhat predictable, and it only occupies a fraction of each animal’s life (herbivores spend most of their time grazing and larger carnivores may sometimes go days without hunting). As herbivores get brainier they might become more cautious and vigilant about carnivores, or more stealthy, but when it comes to escaping from one that is chasing you, about all you can do is run faster, and maybe bob and weave with greater flair. The same holds for the carnivores, and the predictability in both animals’ behavior means that they can be controlled by relatively simple genetic programs that employ rules of thumb or algorithms to get their jobs done.

On the other hand, rule-based behavior such as in these examples works less well when the thing to be anticipated is itself flexible and imaginative in its behavior. When this happens, natural selection is presented with a moving and unpredictable target, and this often means building in redundancy and complexity because now the possibilities multiply endlessly. For example, primates have evolved more complex social behavior than most other animals. They live in societies with fluid dominance hierarchies, complex and shifting networks of relationships and coalitions, power brokering and conflict resolution, and many repeated interactions over long periods of time. Now, instead of a brain following simple rules, it becomes necessary for it to look ahead, to consider alternatives, and weight them according to their probabilities of success at the particular time and place. The sheer number of possible contingencies and outcomes means that the old rules have to give way to broad strategies that must be constantly modified in the light of recent information. Success in these complex societies goes hand-in-hand with social success, and this means being good at using and manipulating those around you: if you have more friends than I do, when it comes to a fight, you will have more people on your side; if you have more friends, someone might be more attracted to you as a mate, or less likely to challenge you; if you are going hungry, I might be more likely to help; or if you are unwell, I might be more likely to remove ticks from your fur.

The primatologist Alison Jolly writing in 1966 and the psychologist Nicholas Humphrey writing in the 1970s suggested that in these kinds of complex social societies, any trait that allows you to outwit your neighbors in this social competition will grant benefits and soon spread to your offspring and theirs. To remain competitive, others must match your social sophistication with their own; and when this happens, the species is set off on a social arms race in which increases in social intelligence in some must be matched by increases in others. This is almost certainly a genetic rather than cultural evolutionary process. The reason is that social intelligence, unlike watching someone make a better hand ax, is not easy for someone else simply to imitate or teach to others, because the situations in which it is used never appear twice in exactly the same form. If you can’t simply copy social intelligence, then your only alternative is to become a social innovator, working out for yourself how to manipulate society, and this requires a big socially intelligent brain.

This is just the opposite of what we concluded for inventiveness, where most of us can get by just fine copying others. Humphrey and Jolly were aware that the nature of human societies also meant a new hostile force emerged in our lives—other humans. Humans increasingly had to deal with other fellow humans whose ingenuity in social matters and desire to manipulate society grew with their increasingly large brains. We got locked into a back-and-forth struggle with each other’s minds, and these minds presented a constantly shifting and unpredictable target. It was an arms race that can be likened to the arms races between our immune systems and the viral and other infectious diseases they attempt to thwart. Diseases such as colds, influenza, malaria, or HIV all change in unpredictable ways governed only by the number of different configurations of their genes, and this is an effectively infinite number. Even today, no one can predict how these diseases will change from year to year. If we could, we could prevent epidemics. Our immune systems dedicate trillions of cells of every variety they can muster, each one trying out some new configuration on its cell surface in an attempt to recognize and destroy the invaders. The only other single organ of such complexity and investment might be our brains.

But our brains must do even more: rather than merely playing a defensive game as our immune systems do, our brains attempt to stay one step ahead of their rivals, and this means getting inside their minds to try to anticipate what they might do next. It becomes necessary to develop what have been called “theories of mind”—a sense of knowing what you think another animal knows, and being aware that it is having similar thoughts about you. Our brains can effortlessly think about situations like “I know that she wants to buy that work of art.” Psychologists call this first-order social intelligence. With a little more effort we can think, “I know that she wants to buy that work of art, and that she knows I am thinking I want to buy it.” This second-order intelligence can easily extend to a third level in the form of “I know that she wants to buy the art, and that she knows I am thinking I want to buy it, and that she is aware that I am aware of her desire to buy it.” Some psychologists say that some of us can routinely deal with even higher-level orders of social intelligence! But what is most revealing about stating them in a sentence is that it makes the mental calculations sound torturous and lengthy but this is something we do almost without thinking.

This pressure to be able to think about and imagine what is going on in the mind of your competitor may have been the force that gave rise in humans to what we now recognize as our conscious minds. With consciousness, an animal can “bring to mind” the things it ought to be thinking about, consider alternatives, and devise plans. In
The Selfish Gene
, Richard Dawkins suggested that consciousness might have been the final stage of animals becoming ever better at simulating in their own minds what must be going on in someone else’s mind, and then sifting among the alternatives that the simulation throws out. Ultimately to make the simulation complete it must include a model of itself interacting in the world it is attempting to simulate, and
poof
, this is self-awareness. (Dawkins cautioned not to take this idea too seriously because he thought it might lead to an infinite regress. The difficulty is that if consciousness arises from some virtual observer who reads and interprets the simulation, how do we account for that observer? The answer might be that a simulation of oneself needs another to “see” it, and so on.)

The “persistence hunting” style of the San Bushmen of the Kalahari Desert might be a case of humans using mental simulation to great advantage over a less intelligent adversary. San hunters use a combination of running and tracking to pursue their prey across the South African veld, and this can require them to run many miles for extended periods of time. Endurance running of this sort is only seen in humans, and is thought to have been one of the earliest forms of human hunting, having evolved perhaps as early as 2 million years ago. If true, it could go some way toward explaining why humans seem to be so good at running long distances in marathon foot races. Among the Sans’ favorite large prey are the kudu and eland, both of which are large grazing animals that can stand over five feet at the shoulder. Like most large grazing animals, kudu and eland have evolved to escape from predators that can put on bursts of speed, but not run long distances. This makes them vulnerable to the San who, remarkably, seem capable of keeping up their dogged pursuit in the hot sun in hunts that can last sometimes eight hours, eventually running their prey to exhaustion.

Now, the link to mental simulation is this. Like any hunter, the San creep up on their prey in an attempt to surprise them. Normally they are spotted and the animals move off by trotting away to a safe distance. The San continue to pursue them this way, forcing the animals repeatedly to move, tiring them out. Sometimes the animals move far enough away that the San lose sight of where they have gone. When this happens, the San are forced to follow the animals’ tracks. On some occasions they even lose the tracks and it is at these times they seem to rely on a mental simulation to work out where the kudu have gone. San hunters report that they try to think like a kudu (or eland) would think. They will get down on all fours and try to put themselves into the mind of a kudu, even reenacting how it might behave in an attempt to work out which direction it has gone. If this works, and their simulation leads them to the animal, it might move off again. The hunt then becomes a test of who will collapse first, the man or the animal. But the man always has the one-sided advantage of his mind simulation. Just imagine if the eland or kudu could think like him.

Of course, other humans do have the ability to simulate what is going on in their adversaries’ minds. When competition among brains is fierce, as is suggested by the idea of an arms race, there are many losers, and so it would not have been sufficient merely to keep up: one had to stay among the leaders to survive. If, as we have imagined, the competition was mainly centered on this newly emerging consciousness and sophistication in social and psychological traits, the sieving or filtering out of survivors from non-survivors each generation would have sorted people most strongly by their brains, rather than sheer brawn. Among the evolving human lineage, a social and psychological arms race provides a plausible mechanism, then, not just for the enlargement of our brains but also for the rapid pace of that enlargement over time. Increasingly, the survivors would have been those able to deploy sophisticated psychological strategies emboldened by strongly perceived emotions, and able to engage in strategic and fluid coalitions. These would have to be met by yet more sophisticated strategies in others.

Once a species starts evolving along this trajectory, it might be difficult or impossible for other similar species to keep up. This might then also provide the answer to a question that has long puzzled anthropologists: why we alone emerged as the sole survivor of our lineage, and why no other species acquired intelligence like ours. The other
Homo
species that had been spawned along the way, including
H. habilis, H. erectus
,
H. ergaster,
H. heidelbergensis
, and
H. neanderthalensis
, would each have had to compete with the next large-brained and shrewd species that was about to emerge; perhaps that next one just got one step ahead and the others never recovered. It has even been suggested that our dominance of our particular niche in life is what kept chimpanzees from moving on from theirs. As for the rest of the animal kingdom, few have entered the social corridor the primates did which set our social competition into overdrive.

THE DNA THAT MAKES US HUMAN

IF THIS
story about our emerging brains is broadly correct, then we might expect to find genes that cause our brains to enlarge but also change the nature or structure of our brains, not just add more brain material. A computer with more processors is not necessarily cleverer than one with fewer processors, just faster. The publication of the entire sequence of the human genome in 2001 made available a list of our genes. This alone was of limited value for understanding our evolution. But as similar lists became available for other species, it became possible to ask questions about which of our genes differed most from them. The answers display the exquisite precision with which natural selection can sculpt our genes, even though it only gets to see their actions via our behavior.

Darwin’s great idea of “descent with modification” teaches us that these comparisons can be used to answer questions about what has happened along an evolving lineage of species over vast stretches of time. Darwin realized that species evolve and give rise to one or more daughter species that then go on to do the same. This means that any pair of species we care to examine will have, at some time in their past, shared a common ancestor from which they both descend. If we wind the clock of evolution back around 300 million years, a species existed that, although no one would have known it at the time, would become the common ancestor to both present-day mammals and birds. A comparison of the same gene in a contemporary bird and a contemporary mammal then records the evolutionary changes that have occurred in one of these lineages, plus those in the other, or 600 million years altogether.

If we wind that clock back just 6 million years or so, we find the species that was the common ancestor to ourselves and chimpanzees, and this is why comparisons between these two species are so informative about the question of what makes us genetically human. But the task of finding differences between humans and chimpanzees is made daunting by two factors. One is that both species have about 3 billion of the chemicals called bases or nucleotides that make up our DNA genetic code. These 3 billion bases are strung out along the structures we call chromosomes. Worse, we are about 90–95 percent identical to chimpanzees in the sequence of these bases along the chromosomes, and more like 98–99 percent in the sequences that we call genes—sequences that carry the codes or instructions for making proteins. What this means is that in the 12 or so million years that separate the two living species (6 million years each since our common ancestor), only about 1 percent of our protein coding DNA has changed.

Still, powerful computers make it possible to check these billions of bases, and when they were checked for humans, forty-nine regions of our genome emerged in which the pace of evolution had dramatically accelerated in our lineage compared to chimpanzees and to other animals. The regions were called
Human Accelerated Regions
, or
HAR
s, and they should be the Holy Grail genes that make us human, the parts of our genome that really distinguish us from chimpanzees. This is because accelerated change is an indicator that natural selection has been acting particularly strongly on a gene. It means that each time some new helpful variant has arisen, it has quickly spread through the population until everyone has it, and then this process has been repeated as new and different variants arise.