Wired for Culture: Origins of the Human Social Mind (10 page)

The significance of this achievement is appreciated when we recognize that any proper history of life on Earth is a history of death, and the reason is the rule of two. The rule gets its name from the fact that throughout history, females—of plant and animal species—have left, on average, just two offspring that will survive long enough to do the same. Some have left more, others fewer, but the average is roughly two.
It is a surprising statistic because, for example, a female rat has a prodigious ability to make more rats: she reaches maturity at about thirty-five days old, she can produce a litter of up to twelve pups, wean them in a month, and then start all over again, breeding year round until she dies, typically at two to three years. This high output is true of most small animals. Indeed, the rabbits’ impressive reproductive potential is immortalized in the phrase “breed like rabbits.” But even then, a typical female rabbit leaves just two surviving offspring.

A larger animal like a female elephant takes longer to reach maturity—around ten years—and when she does reproduce it is one at a time, and it takes her far longer to rear her offspring before she can reproduce again. But female elephants reproduce into their sixties, and so they also tend to leave about two surviving offspring. The same is true even of those wildly fecund organisms the trees. An oak or chestnut tree that lives for centuries and rains acorns and chestnuts down in our forests and on our lawns and streets could produce millions of offspring in its lifetime, but oaks and chestnuts on average leave just two surviving offspring trees. Go outside and stare at the vast trunk of one of these trees—some weighing hundreds of tons—and all its many branches. It is a sobering thought that all of that effort in making the wood, and in producing all of the tree’s bark, branches, and leaves over so many years, comes to so little.

This rule of two turns out to have a simple explanation that tells us it could not be any other way. For every offspring of a female, a male has been involved (the rule of two becomes the “rule of one” if we have in mind asexual species that reproduce on their own). If a male and female produce two surviving offspring before they die, those two replace this male and female. If this male and female were to leave behind even just three offspring, and each of these three in turn produced three that survived to reproduce, and so on, the numbers of this species would increase without end. Consider just a population of fifty males and fifty females in which each of these females produced three surviving offspring. In the first generation, the 50 females would produce 150 surviving offspring (three each), increasing the population size by 50 once both the parents had died. These 150 would in turn become 225 when each of the 75 females in this generation left behind three offspring. It is easy to see that the world would quickly become covered in layers of rats, or rabbits, and even only slightly less quickly in a layer of elephants if they could break the rule of two. If oaks and chestnuts could leave more than two, our world could become forests of these great trees. The capacity of common bacteria to reproduce is so great that if their growth went unchecked we would in a matter of days (or less time) all be standing up to our waists in a mat of bacteria that carpeted the entire world.

We learn three lessons from this. One is that for most species the difference between the numbers of offspring they produce and the numbers that survive is so large that it is not much of an exaggeration to say that all offspring ever born die before they get a chance to reproduce. Such startlingly high levels of mortality are the same as saying that competition for survival is fierce. It is this competition that lies behind the nineteenth-century philosopher Herbert Spencer’s summary of Darwin’s evolution by natural selection as “survival of the fittest.” Those few of us who have survived are well adapted: we are the rare descendants of a long line of other rare survivors who were our ancestors. The genes in our bodies and those of every other organism are those that have survived for millions or even in some cases billions of years because they were good at producing successful
vehicles
, while uncountably greater numbers have died trying. This means we can expect the genes we see today to be very good at promoting their interests, and they will do so by means of the ways they vary the bodies they produce. But even with all this fine-tuning, the average female still produces just two surviving offspring.

The second thing we learn is that different organisms have adopted different tactics for trying to break through the two barrier. Some—like oak trees and rabbits—go all out. Others, like elephants and whales, show more restraint, but put more effort into each offspring.

The third thing we learn is that all those different ways of producing offspring, some as rabbits, others as trees, are just different but approximately equally good ways of making vehicles for transporting genes into the next generation. All that time, bulk, energy, and trillions of individual cells required to make an adult elephant yield the same number of surviving offspring averaged over long periods of time as a rabbit, or even a single-celled yeast (of which there are, technically, not males and females, but two mating types called
α
and
a
). Nearly every cell that resides inside a complex organism like a tree or ourselves never sees the light of day, laboring away instead to propel a small number of others into the future. It is even starker than this. The egg of a female and the sperm of a male are single cells. We could say that the trillions of cells that make up our bodies spend a lifetime devoted to seeing just two of their kind escape into the next generation.

It is easy to read this as demonstrating that animals act for “the good of the species,” holding back so as not to overpopulate. But the truth is nothing of the kind. Occasionally, a species will break the rule of two for short periods of time. If a more fecund female came along who could on average leave three surviving offspring, or four for that matter, natural selection would favor her: her greater number of surviving offspring would gradually come to dominate the population in which she lived, and eventually all females would be of her kind, able to trace their ancestry ultimately back to her. But if this happened, this species’ overall numbers would rapidly increase and two things would follow. One is that at some point the species would reach what is called its “carrying capacity,” a number that attempts to describe how many individuals of a species the environment can support. If the population expands above the carrying capacity, some of the excess individuals will die of starvation. The other is that this species’ increased numbers would mean that its predators would come to enjoy a bounty of prey and their numbers would thereby increase. The combination of running out of food and the extra predators would reduce the average number of surviving offspring from the superfemales back to two.

Some species can break the two barrier for short periods of time when they have just evolved or when they are introduced to a new area. A newly evolved species that consisted of just a single male and female would have to break the barrier ever to increase in numbers. So, the surviving species we see around us have broken the barrier at some point in their history. But these species will now be at their carrying capacity and leaving on average just two surviving offspring. When rabbits were introduced to Australia, they bred like rabbits. The Australian environment had not had rabbits before, and it is likely that the diseases that kill other small Australian animals did not affect them. But the growth of rabbits was soon contained by introducing a virus that controlled their numbers by killing some of them and making others weak or ill.

Now another newly introduced creature—the cane toad—is eating its way across Australia. It seems unstoppable because its poisonous skin either kills or repels the native Australian predators. These cane toads will eventually reach their carrying capacity, and other animals are already discovering how to avoid their poisons. Some field biologists report that the kookaburra has learned how to flip the cane toad over onto its back before eating it, to avoid the toxic skin. If this strategy succeeds, kookaburras will also probably leave more than two surviving offspring, at least for a while, and Australia will ring to the sound of kookaburras even more than it currently does.

Nature is never quite as tidy and predictable as these examples suggest, but the rule of two is what we often call the balance of nature, and it is how things have worked for billions of years. That is, until a species came along that discovered how to break this rule and do so over long periods of time. Once again, that species is human beings, and for at least the last 80,000 years or so we have carpeted the planet with our excess offspring, and continue to do so. Our discovery for breaking the rule of two was to build cultural survival vehicles. The Earth had not seen the likes of this before or since, and this is the sense in which we saw in the Introduction that culture became our species’ biological strategy. Here was a force that could not only deploy technologies such as fire, clothes, and shelter to adapt different environments to it but has been able throughout its history repeatedly to produce innovations that reset the world’s carrying capacity to hold more people in a given area. Plagues, wars, and droughts, and the occasional collapse of civilizations, have at times slowed our march but as yet not stopped it.

We didn’t break the rule of two only by altering the carrying capacity: modern human women achieve a higher birth rate than other large Great Apes. As a rough estimate a wild chimpanzee female might give birth once every four to six years. The comparable figures for gorillas and orang-utans are once every four to five and once every six to nine years, respectively. By comparison, human women living in hunter-gatherer groups might have had a baby about every three to four years, and a two-year gap is common in modern societies. Human women also maintain a longer
reproductive lifespan
than these Great Apes, reproducing for around thirty years of their lives. This is nearly double that of a gorilla, ten years more than a typical chimpanzee, and perhaps five years more than an orang-utan.

Our rapid rate of reproduction might owe something to a peculiar feature of our species. Human women have a long period late in their lives when they don’t reproduce, called the
menopause
. Many people simply assume that the menopause is a consequence of our living longer, and that in our “state of nature” women would not have lived long enough for it to occur. But this idea has in more recent years given way to an intriguing suggestion. It is that the menopause might have evolved as an act of nepotism or help directed at relatives. Natural selection might have favored women who ceased their own reproduction late in life to help their daughters or their daughters-in-law to reproduce, rather than compete with them. Those who advance this idea, known as “the grandmother hypothesis,” suggest that having an extra pair of hands around would have meant that the daughters or daughters-in-law could reproduce more quickly. Natural selection would have favored this period of menopause if by helping her daughter or daughter-in-law this grandmother eventually gained more grandchildren than she would have had she chosen to continue to reproduce herself.

Another possibility is that human women have been able to maintain a higher reproductive rate than other Great Apes and still provide for their young simply because modern human societies from early in our history have been more efficient at providing food, shelter, protection, and other resources for people. Whatever the reasons for our higher growth rate, reproduction is to the growth of populations what interest is to money. Populations grow by compounding themselves as the babies born now grow up themselves to have children. So, this higher total reproductive output of our species along with our ability to control our environments has meant that wherever human groups ventured, they would likely have filled up their space and found themselves in constant and intense competition with other human groups doing the same. This tells us that competition among cultural survival vehicles throughout our history has been intense, and just as is true of our genes, those that have survived will have acquired traits that make them good at promoting their inhabitants’ survival. For nearly all of our history up to sometime around 80,000 years ago, we were like other animals and we barely increased in numbers. The species that immediately preceded us,
Homo erectus
, the Neanderthals, and even so-called premodern or archaic
Homo sapiens
, struggled to replace themselves and then went or were driven extinct. As recently as 20,000 years ago, our numbers may have amounted to just a few millions, maybe fewer, in the world. But our growth has been rapid, and especially so in the last 10,000 years, with over 6 billion of us today. It is all down to social learning and our distinct cultural survival vehicles.

CHAPTER 2

Ultra-sociality and the
Cultural Survival Vehicle

That even a disposition to die for our cultures can be adaptive,
just as it can be to fight to the death for your own body

VISUAL THEFT

W
E HAVE SEEN
that by sometime around 160,000–200,000 years ago our species might have acquired the capability to learn new behaviors from watching and imitating others. This put us on a trajectory of cumulative cultural evolution as ideas successively built and improved on others. It is something no other species has achieved, and it continues today at ever-increasing rates because the sheer volume of cultural knowledge acts as a vast crucible for innovation. We need look no further than the chairs we sit in, the televisions we watch, the books we read, the cars we drive, the computers we work on, the spaceships and high-energy physics laboratories we produce, or even the food we eat, to see its effects. And so, to most commentators social learning is “job done,” “end of story”—our species could make things, so we have prospered in a way that other animals didn’t. But in fact our acquisition of social learning was just the beginning of our story as a species because it would create a social and evolutionary crisis, the resolution of which would lay the foundations of our psychology and social behaviors and determine the future course of the world.

Here is why. Social learning is visual theft. If I can learn from watching you I can steal your best ideas and without having to invest the time and energy that you did into developing them. If I watch which lure you are using to catch fish, or how you flake your hand ax to give it a sharp edge, or secretly follow you to your hidden mushroom patch, I am benefitting from your knowledge and ingenuity, and at your expense because now I might even catch the fish before you do. Social learning really is visual theft, and in a species that has it, it would become positively advantageous for you to hide your best ideas from others, lest they steal them. This not only would bring cumulative cultural adaptation to a halt, but our societies might have collapsed as we strained under the weight of suspicion and rancor.

So, beginning about 200,000 years ago, our fledgling species newly equipped with the capacity for social learning had to confront two options for managing the conflicts of interest social learning would bring. One is that these new human societies could have fragmented into small family groups so that the benefits of any knowledge would flow only to one’s relatives. Had we adopted this solution we might still be living like the Neanderthals, and the world might not be so different from the way it was 40,000 years ago when our species first entered Europe. This is because these smaller family groups would have produced fewer new ideas to copy and they would have been more vulnerable to chance and bad luck.

The other option was for our species to acquire systems of cooperation that could make our knowledge available to other members of our tribe or society even though they might be people we were not closely related to—in short, to work out the rules that made it possible for us to share goods and ideas cooperatively. Taking this option would mean that a vastly greater fund of accumulated wisdom and talent would become available than any one individual or even family could ever hope to produce. That is the option we followed, and our cultural survival vehicles that we travelled around the world in were the result.

We take this cooperation for granted in our modern world, but it rests on a psychology and social behaviors new to evolution, and unique to our species because no other animal has confronted the crisis of visual theft. Consider that even the simplest acts of exchange among unrelated people wobble on an unstable tightrope, because now my instincts to take advantage of you will not be held back by the usual bonds of family ties. This is because when I help a relative I help a little genetic bit of myself, and so natural selection favors my nepotism
so long as the help I provide to them is not too costly. It also means I have less incentive to cheat that relative, or for them to cheat me. When we watch a streaming mass of ants mount a suicidal charge out of their nest to take on some foe, we admire their unflinching courage, but we recognize these ants are dying to save their brothers and sisters, and especially their queen. She is the source of additional copies of their shared genes, produced in the form of more brothers and sisters. The same logic of what evolutionary biologists call
kin selection
tells us why your skin cells are happy to die to protect you from the penetrating and deadly rays of the sun. These skin cells are all genetic clones of each other, only too happy to die if this makes it more likely the body they inhabit will reproduce one day.

But the hallmark of modern human tribal societies was that they were not limited to relatives, and this meant that evolution had to confront the problem of having a potentially unruly mob of individuals on its hands, each looking out for their own well-being. The difference is everything. Now anything I do for you might benefit you and your genes, but at my expense. In fact, once people started living together in groups, natural selection would have favored a raft of
selfish
psychological ploys for taking advantage of others’ good nature, because there would have been a continual conflict between what was best for you and what was best for your group. I might take more than my share from the dwindling grain store when you are not looking, or attempt to convince you that I am hungrier than you when food is scarce. I may “forget” in future to return a favor, I may try to escape your attentions, I might return less of a favor, or plead poverty. I might lag behind out of harm’s way in battle, or I might get angry if you try the same, and spread rumors that you are not to be trusted.

Left unchecked, these ploys would have caused our societies to collapse before they got off the ground. To make our societies work, then, we had to acquire the social and psychological systems that could somehow overcome and tame selfish instincts born of millions of years of evolution by natural selection to cheat, exploit, dupe, and even murder one’s rivals. The solution was simple in principle but profound in its effects: natural selection found ways that made it possible for individuals to align their interests with those of their group. If the benefits of the cooperation that might flow from this alignment could exceed the returns from acting on pure self-interest, cooperation, even with non-relatives, begins to make sense. Maybe you show great courage in battle and this makes it far more likely your group triumphs over an aggressive foe. If as a consequence you are also more likely to survive, this apparent altruism is a good strategy for you. Or maybe by virtue of having some skill that you share with other members of your group, like being good at making spears or at navigating on the open seas, you acquire a value to the group or a reputation that makes people treat you more charitably. If the collective action you inspire, or the benefits you can bring to the group, can return more to you than behaving selfishly, then your apparent altruism is really a case of enlightened self-interest, and the usual conflict of interest between what is best for you and what is best for the group can vanish.

In fact, the monumental and even sometimes terrifying achievement of human culture has been to discover how to get groups to act together in a coordinated way. It is monumental because by unlocking the psychological means to pool our efforts and skills, it granted our societies a formidable degree of shared purpose that could be put to use in solving the problems of survival. At the same time, aligning individuals’ interests with those of their groups could be terrifying in making our cultural survival vehicles formidable competitors against other groups that might be competing for the same territories. Now, someone could forage while another hunted, someone could mend sails while another plotted a course, two could stand guard with sharpened spears while a third steals a competing tribe’s animals, and my army could cross the valley and attack yours, or repulse it when you attack me.

As I mentioned in the Introduction, the distinctive and salient feature of much of our social existence is the sense of belonging to a cultural group toward which we feel an allegiance that we often do not easily extend to others outside of that group. That sense is the emotion natural selection has kindled in us to get us to behave as a group with a shared purpose. The unusual psychology it brings us can even extend to getting us to engage in costly altruistic acts that rival those of the social insects—the ants, bees, wasps, and termites. Who, for example, can forget images of Japan’s fabled World War II Kamikaze pilots, or the warriors in World War I streaming out of the trenches “over the top” to die in battle? You will take this cooperative psychology entirely for granted because it has been wired deep into your DNA, but no other animal does anything like this. You will never see a group of horses or a group of chimpanzees streaming out “over the top” to die for each other. No lion or zebra holds doors for one another, no ape ever politely stood in line; they don’t look after the elderly or help those in distress. It is true, elephants are sometimes described as “grieving” for a dead member of their group, but this behavior is normally directed at relatives.

If the social insects are sometimes described as
eusocial
, or truly social, humans have uniquely among the animals achieved a
hyper-
or
ultra-sociality
. This label acknowledges that our altruism has broken free of acts aimed merely at helping relatives. In this chapter we will even see how our evolved cooperative psychology can admit a disposition toward suicidal self-sacrifice. Surprisingly, confusingly, and seemingly paradoxically, it will be shown to be in an individual’s self-interest to have this disposition. At the same time, a troubling feature of the way this disposition evolves is that it can cause us to treat people from other societies, and sometimes from even our own, crudely and violently. That is the fragile nature of our sociality and psychology, and it arises because our cultures are cooperative vehicles for the survival of unrelated people, and their genes.

VEHICLES AND THE DISCOVERY OF COOPERATION

THE ORIGINS
of human cooperation can be traced to developments in the earliest replicators that populated the Earth beginning perhaps 3.8 billion years ago. The earliest replicators were probably
RNA
molecules or
ribose nucleic acids
, a simpler form of the DNA molecule or
deoxyribose nucleic acids
, whose twin strands elegantly intertwine in a twisting helical shape. Nearly 4 billion years ago, the biotic world of the very young Earth may have comprised little more than naked replicating segments of RNA floating in a warm primordial soup. Molecular biologists call this the
RNA-world
, and RNA may be the ultimate or
ur-
ancestors (meaning the original or earliest form) of all life on Earth.

One of the more remarkable discoveries during the early years of molecular biology in the 1960s was that strands of RNA all on their own can have distinctive shapes or what biologists call
phenotypes
. Whereas all DNA molecules have more or less the same shape, strands of RNA that differ in their chemical makeup of nucleic acids fold and twist into different forms. This discovery about RNA gave molecular geneticists a mechanism for the early evolution of life on Earth. It turns out that the different shapes can influence the survival of one strand in competition with others. Some shapes are, for example, more resistant to being pulled apart by water. An RNA strand with the right chemical makeup to adopt one of these shapes will live longer and therefore tend to accumulate in competition with RNA strands more easily pulled apart. The RNA strand itself becomes a kind of phenotype, and its own survival vehicle.

The early biotic world was probably one of competing strands of these simple replicators of RNA, and whichever strand was lucky enough to escape the forces of nature and find enough chemicals to replicate itself would have dominated. But there would have been only so many different shapes. At some point, two strands of RNA—competitors for the same chemical resources—might have discovered they could physically combine to make a new kind of shape. This transition would have produced the first
vehicle
comprised of more than one replicator, and it would have increased the complexity of life. But the question is why would this new cooperative venture work? On their own, each of these strands could replicate whenever it wished, but together they would have to give up some of this freedom. Why, for example, should I join forces with you to pick apples when I can pick them on my own, or better yet steal from you?

One of the great insights of evolutionary biology has been to understand how entities that would otherwise compete can be tamed or domesticated to form alliances that serve both. John Maynard Smith and Eörs Szathmáry have called these the “major transitions” in our evolution, and two RNA strands joining together might have been the first of these major transitions. Perhaps the two strands of RNA could help each other to duplicate or copy themselves, or perhaps they could better avoid being pulled apart by water. Living longer would have given this new joint vehicle more chances to replicate itself. We can see from this a reason to give up some of your freedom and to cooperate with a former competitor: your joint enterprise can work if the payoffs more than offset the loss of the freedom to act alone. I should join forces with you in picking apples if we get more than twice as many together as we do separately. Even so, why shouldn’t I wait until we have accumulated a large number of apples and then run off with them?

The first of the evolutionary transitions unfurled the first partnership, and the world of evolution never looked back. Once two or more replicators can combine to produce a vehicle that gives them better returns than they would get from competing, their fates become linked, and it is this linkage that can tame their instincts to compete with or exploit each other. Now the answer to why I should not run off is clear: to give up on the partnership is to give up some of its riches from future returns. Once fates are linked, replicators acquire a new incentive: to become better and better at what they do because now they have less reason to fear betrayal. They can specialize in ways that promote the partnership even more. Maybe if we join forces to pick apples and you are stronger than me, I should specialize in standing on your shoulders and you should specialize in supporting me.