The Social Leap

What’s less obvious is the role that evolution played in shaping our psychology. We tend to think of evolution in terms of anatomy, but attitudes are just as important for survival as body parts.
As is apparent in our fear of the dark, our motivations evolved to help us survive and thrive. That means that bad feelings serve an important purpose, but so do good ones.
By studying mutation counts in the DNA of body lice and head lice (which are closely related to each other but not to pubic lice), we have pretty good evidence that our ancestors stopped running around naked at least seventy thousand years ago.
The most common way that animals who live in small groups solve this potential inbreeding problem is by having either males or females leave the group in which they were born when they reach adolescence.
Such people often believe that if genes influence the contents of our minds, those aspects of our minds that are subject to genetic influence are impervious to environmental or social influences and are outside personal control. I want to clarify that nothing could be further from the truth.
Yet studies of hunter-gatherer eyesight show that there are almost no nearsighted hunter-gatherers.
People who have myopia genes and live in modern environments usually develop nearsightedness; people who have myopia genes but live as hunter-gatherers almost never do. So even effects that are largely genetic can at the same time be largely environmental.
Our genes nudge us in certain directions—sometimes this nudge might more aptly be described as a shove—but we make the decisions that determine the trajectory of our lives.

The bottom line is that evolutionary psychology is a story about how evolution shaped our genes, which in turn sculpt our minds, but it is not a genetically deterministic story at all. The environment also sculpts our minds, and our culture, values, and preferences play a critical role in who we become—and where we go next.

These experiences suggest how our ancestors might have responded to the threat of predation on the savannah: by throwing stones, particularly if they could band together and throw lots of them.
Among experienced throwers, arms and shoulders are just a small part of the equation. Power throwing begins by stepping forward with the opposite-side leg (e.g., a left foot step for a right-hander), progresses through rotation of the hips, followed by rotation of the torso and then shoulders, and finally the elbow and wrist follow through.
These sequential motions take advantage of the fact that the combined forward and rotational forces of the body stretch the ligaments, tendons, and muscles of the arm and shoulder, which accelerate the arm forward at the very end of the throw, like the snapping of a rubber band.
Nonetheless, throwing can be incredibly effective if you practice a lot.
Consider these three historical accounts that anthropologist Barbara Isaac dug up for her wonderful article “Throwing and Human Evolution.” In hardly any time at all they had so badly beaten us that they had driven us back into shelter with heads bloodied, arms and legs broken by blows from stones: because they know of no other weaponry, and believe me that they throw and wield a stone considerably more skillfully than a Christian; it seems like the bolt of a crossbow when they throw it.
Many a time, before the character of the natives was known, has an armed soldier been killed by a totally unarmed Australian. The man has fired at the native, who, by dodging about has prevented the enemy from taking correct aim, and then has been simply cut to pieces by a shower of stones, picked up and hurled with a force and precision that must be seen to be believed... the Australian will hurl one after the other with such rapidity that they seem to be poured from some machine; and as he throws them he leaps from side to side so as to make the missiles converge from different directions upon the unfortunate object of his aim. —John Wood, 1870
Once Australopithecines learned to fend off predators by throwing stones, they would have soon discovered that they could also hunt via collective stone throwing.
The greatest challenge to cooperation is free riding, or the tendency to skip the hard work while sharing the benefits.
Ostracism and rejection have remained important tools for enforcing cooperation through to the present, and as a result we still find social rejection incredibly painful and do whatever it takes to stay in our group’s good graces.
The ability to kill at a distance is the single most important invention in the history of warfare, because weaker individuals can attack stronger individuals from a position of superior numbers and relative safety.
For this reason, many scientists have adopted the social brain hypothesis, which is the idea that primates evolved large brains to manage the social challenges inherent in dealing with other members of their highly interdependent groups.
If you look at a chimp’s face, you can’t really tell where it’s looking without closely inspecting its eyes. In contrast, humans have evolved white sclera, which clearly advertise the direction of our attention.
Chimpanzees are far more self-oriented and far less group-oriented than we are, which is why they struggle to work effectively as a group.
But once we moved to the savannah and found that cooperation was the key to success, we had the good fortune that group goals and individual goals aligned for the first time in the great apes.
When our ancestors chanced upon a social solution to the challenges of life on the savannah they set in place a cascade of events that eventually led to our human origins, which is why I describe our move from the rainforest to the savannah as the “social leap.”
Most important of all, our social leap also transformed the evolutionary pressures on us. In response to the risks and opportunities inherent in our new life, we dramatically changed our mental proclivities and expanded our cognitive capacities over the next several million years.
Not only did Homo erectus invent better tools, but the evidence suggests that they were the first species to plan for a world beyond their current needs.
It seems odd, but monkeys and apes are incapable of planning for future needs they do not currently feel.
Carrying a club or spear is a lot easier when you can free your hands from walking, which would have motivated Lucy and her ancestors to walk upright.
With division of labor, animals that were once our predators were now our prey.
Despite having guts larger than ours, our fellow great apes cannot extract enough calories and nutrients from their diet of raw food to sustain a brain nearly as big as ours. Not only is our brain-to-gut ratio much greater than that of the other apes, but we also burn calories faster than they do. Cooking our food allowed us to evolve a faster metabolism to support such a large brain.
Finally, cooking freed our ancestors from the incessant chewing required by raw food. A typical chimp day involves about eight hours of chewing to soften food before it can be effectively digested.
The Pacific Islands were the last places to be colonized, with New Zealand coming in last place, only 700 years ago.
Storytelling may have been another by-product of the control of fire, as the conversations of hunter-gatherers during the day differ notably from the stories they tell around the fire at night.
During the day, people spend most of their time talking about ongoing social concerns and matters of economic necessity. But once night falls, communal fires are lit, and people gather in small groups, conversations blend into stories, and stories often reveal important lessons about how to live one’s life and follow cultural rules.
The importance of cumulative culture can be seen in almost every aspect of our lives, but one of the clearest examples can be found in the harrowing tales of early European explorers to the Arctic, Americas, Africa, Australia, and Asia. On countless occasions, intrepid and well-prepared adventurers perished or nearly died, while just around the corner, indigenous people who lacked their modern technology were well fed and sheltered. It was our capacity to learn from the experiences of others that gave Homo sapiens an enormous local advantage, with new strategies and innovations built on a platform of prior discoveries.
As a consequence, each generation had no need to reinvent the wheel, and a child could acquire an understanding of the world that a few generations back would have been available only to geniuses.
our ancestors faced were trivial by comparison.
Being a hunter-gatherer might seem like an idyllic and carefree existence, but it was riskier than living in the scariest neighborhoods of the most dangerous cities today.
The best way to predict other people’s behavior is to know their reasoning and goals, so we evolved Theory of Mind: the understanding that the minds of others differ from our own.
We feel guilt when we’ve harmed someone in our group, and the negative self-directed feelings associated with guilt help us learn from the experience and avoid doing it again (before our friends give us the heave-ho).
Shame is felt when we’ve done something to devalue ourselves in front of our group, and again the negative self-directed feelings ensure that we don’t repeat the shameful behavior and experience further loss in status.
Pride, guilt, and shame are critical parts of being human, and they help us function in the highly interdependent and cooperative groups that emerged with Homo erectus and that have made us so successful ever since.
Chimp mothers do not know what their offspring do not know, and thus are limited in their capacity to teach them (and in their awareness that they ought to teach them).
Over-imitation is an important human propensity, as it allows us to learn to do things even when we can’t fully understand them. By assuming that our teacher knows best, we engage in the highest-fidelity copying we can, which enhances our effectiveness.
Over-imitation has great survival value, as it can facilitate the transmission of complex techniques that are often necessary in the preparation or detoxification of foods.
To tell a lie is to intentionally plant a false belief in someone else’s mind, which requires an awareness that the contents of other minds differ from one’s own. Once I understand what you understand, I’m in a position to manipulate your understanding intentionally to include falsehoods that benefit me. That is the birth of lying.
Researchers have found that they can teach small children to lie simply by teaching them Theory of Mind.
A chimpanzee has a brain that weighs about 380 grams. Three million years of eking out a living on the savannah changed our bodies in important ways, but Australopithecus afarensis’ 450-gram brain was barely larger than that of a chimp. Fast-forward another one-and-a-half million years to Homo erectus, and now our ancestors have a 960-gram brain, twice the size of that of Australopithecus (although they were a fair bit bigger as well, so the relative change wasn’t as dramatic). Another million and a half years later, and Homo sapiens has an average brain weight of 1,350 grams. We added an entire chimp brain onto that of our Homo erectus ancestors. Why did the first three million years of evolution on the savannah give us a paltry 70 grams of brainpower, when the next three million years endowed us with almost a kilo?
The answer to this question lies in the fact that our expanding social capacities led us to evolve greater cognitive capacities to exploit new social opportunities.
The accelerating brainpower that emerged over the last six million years was both cause and consequence of the social changes experienced by our ancestors.
Agriculture emerged about twelve thousand years ago in the Middle East, soon thereafter in China and the Americas, and over the next few thousand years in many other places.
Indeed, some scientists believe that agriculture led us to evolve a tolerance for alcohol rather than a distaste for it, because alcohol killed many of the bacteria that farmers were unintentionally introducing into their own drinking water.
In addition to the diseases farmers caught from their own feces, the animals they kept also proved to be a major source of illness, as human epidemics often have their origins in domesticated animals (e.g., swine and avian flu).
Despite never owning a toothbrush or floss, hunter-gatherers rarely got cavities or gum disease. In contrast, the teeth of early farmers were typically half-rotten, and by medieval times they were utterly foul. Their high-starch, low-variety diet not only resulted in poor oral health, but also led to a decrease in their stature and shorter life spans than were enjoyed by earlier hunter-gatherers.
Hunter-gatherers in “immediate-return societies” (meaning those who eat today what they catch today) typically spend about six hours per day hunting, gathering, preparing meals, and mending tools. The rest of their time is spent socializing and relaxing until it gets dark, at which point storytelling and dancing by the firelight are common activities.
Farming may have been a disaster for individual farmers, but it was a success story at the population level: it allowed large numbers of people to live on land that would have supported only a small group of hunter-gatherers, and it increased people’s reproductive rate.
In contrast to hunter-gatherers, who live each day as it comes, farmers focus on tomorrow. Their labor centers primarily on preparation for the harvest, which is a hugely important and high-effort event.
The free-rider problem is a vicious circle and can quickly destroy a productive community if there is no way to police everyone’s contribution.
Inequality inevitably follows from the demands and opportunities of ownership and stockpiling associated with agriculture.
In contrast to life in the tropics, some hunter-gatherers live in ecologies that enable food storage and also have highly dense, predictable resources. For example, Native Americans who fished for salmon in the Pacific Northwest caught far more than they could eat during seasonal salmon runs, so they dried their catch for later consumption over the winter. This sort of ecology promoted the development of inequality, as families attempted to dominate and defend the best fishing spots during the salmon run. Such families incorporated others by offering some of the fish in exchange for help with the harvest, defense, preparation, and storage of the catch.
With the advent of private property, the rules for provisioning the household changed dramatically.
Hunter-gatherers in immediate-return societies simply cannot support more than one family of children, but private property enables wealthy men to support huge numbers of children.
Numerous princes and kings throughout history have had hundreds of children, with the rapacious Genghis Khan quite possibly holding the world record (with 8 percent of Asia potentially his descendants).
Women’s reproductive potential, in contrast, is not influenced by the number of partners they can attract; a man with twenty wives can have two hundred children, but a woman with twenty husbands cannot. Wealth was important to women because it helped their children survive, but beyond the moderate wealth required for survival, additional resources do not enable women to have more children (although great wealth does give women more grandchildren, through the increased capacity of their sons to attract more partners). Due to these sex differences, wealth was less important for reproductive success for women than it was for men, so men were typically much more motivated than women in their pursuit of wealth. All else being equal, mothers and fathers were also more motivated to pass their wealth on to their sons than to their daughters, again because the reproductive benefits that accrue to wealthy sons are greater than the benefits that accrue to wealthy daughters. Partially because of these sex differences, gender inequality spread across the globe along with private property. Men typically have more power than women in immediate-return hunter-gatherer societies, but women are more equal to men in such societies than they are in other types of foraging or agricultural societies. Agriculture also disrupted gender equity by virtue of the activities involved in preparing the fields and harvesting them. Plow-based agriculture in particular demands greater musculature to work the fields, and hence created a sex-based division of labor, with men working the fields and women preparing the food inside the home.
Once we decided that private property and inequality were acceptable, we started down a slippery slope to all sorts of misery. If it’s okay for me to own more stuff than you do, then it follows that it’s also okay for me to survive and even thrive while you starve.
Thus, the first psychological step away from our hunter-gatherer lifestyle was the willingness to agree that some people are better than others and that inequality is an acceptable outcome. Once you accept that “fact of nature,”
Homo erectus invented division of labor and benefited greatly from it. But the true potential of division of labor can be realized only when people become specialists, spending a lifetime pursuing a particular interest or talent.
First, the safest strategy when dealing with unknown strangers is politeness, and indeed cultures that have high levels of violence often have high levels of politeness. For example, the American South is famous for its politeness and friendliness. But Southerners are also much more likely to react with violence, particularly when they have been treated dishonorably.
For example, talking a big game is more impressive from a stranger, whose stories might be true, than a close associate whom you know to be exaggerating. Similarly, overconfidence on the part of a stranger is typically interpreted as a sign of competence, even though we might roll our eyes when our friends and neighbors show inflated self-views.
When our hunter-gatherer ancestors misbehaved, there was really no way to escape the consequences: gossip ensured that their reputation would catch up with them. In a city, by contrast, it’s easy to exploit friendly and trusting people and then move on before your duplicity is discovered. Modern levels of residential and occupational mobility allow sociopaths to outpace gossip their entire lives.
This challenge is now being met head-on by social media, which is returning us to the close-knit, intertwined lives of our ancestors. Many websites are explicitly designed to communicate reputation.
Uber, Airbnb, and eBay are all business models that rely on the reciprocal transmission of reputation.
Overreactions to bad behavior are a repeated occurrence, with people’s lives disrupted for what were objectively minor infractions.
Imagine a world in which people who wanted to save for retirement were required to find someone of the opposite sex who would agree to partner with them to create a joint account. Imagine further that both parties got to draw equally from their interest-bearing account when they retired, but the rules dictated that for every dollar the man deposited into the account, the woman had to deposit a million. Finally, imagine that people could set up as many joint accounts as they desired, so long as they could find a willing partner of the opposite sex. This is an outrageous set of rules, but if such a world existed, what would you do? Your answer likely depends on whether you’re male or female. If you’re a man, you would probably be happy to establish retirement accounts with any woman with a pulse. With that level of return on your investment, how could you lose? No matter how reprehensible she is, it’s a pretty sweet deal. In contrast, if you’re a woman, you’re in a tight spot. On the one hand, you need to create a joint account so that you can retire with some sort of savings. On the other hand, the rules of the account are stacked against you so strongly that you’re probably going to be very picky when you choose a joint account holder. He’s occasionally grumpy? Forget it. No reason to deal with a difficult joint account holder when there are plenty of nice people out there. He sings off-key? Not worth the pain and suffering. A more tuneful or quieter person will assuredly come along who’ll want to join you. And the list goes on... As is evident in this example, whoever invests more resources into a joint outcome gets to call the shots when it comes to choosing a partner.
In biology, the animal that produces the larger gamete (i.e., sex cell or, in this case, egg) is the female, and the one who produces the smaller gamete (in this case, sperm) is the male. For many animals, producing gametes is the sum total of their parenting effort. The female frog lays her eggs, the male frog sprays sperm across them, and then the two usually hop off into the sunset, leaving their hundreds or thousands of fertilized eggs to hatch into tadpoles and eventually grow up to be big and strong, or perhaps to be eaten by the next fish to swim by. There is no parental effort in such species beyond the act of producing and depositing eggs and sperm, yet even that degree of parenting is a significant investment.
As a result of this biologically mandated difference in parental investment, for every unit of energy that a human male must donate to produce a child, human females must donate much more than a million times as many.
Reproduction is the currency of evolution. If every animal had the same number of surviving offspring, there would be no evolution. Survival is important, but only in terms of living long enough to reproduce and pass your genes on to the next generation.
In this manner, traits and behaviors that are associated with reproductive success become more common than traits and behaviors that are not.
Due to this process of selection, we evolved to enjoy activities that enhance our reproductive success and dislike activities that don’t.
theory. If I live a thousand years but don’t reproduce, my incredible longevity is evolutionarily irrelevant. But if I live long enough to see my
Darwin used the term sexual selection to describe the evolution of those processes that enhance our access to members of the opposite sex.
An honest signal of quality is one that is impossible, or at least very difficult, to fake.
Due to the importance of honest signals, humans are very adept at detecting even subtle cues that indicate quality.
To return to the peacock, its bright color and extraordinary tail are honest signals of male quality because they are an enormous handicap, and that’s why the peahen finds the bright colors and huge tail so alluring.
Bright colors advertise your presence to predators, so female birds can use the brightness of a male’s colors to deduce his quality. A brightly colored bird must be strong and fit to survive looking that way, whereas a dull-colored lad may well be slow and clumsy, and thus would be less suitable as a mate.
Because birds can afford those colors only if their immune system is robust, bright colors (particularly bright reds, oranges, and yellows) are honest signals of internal quality, even though they are being worn on the outside.
Bright reds are inherently honest signals of quality due to the metabolic cost in producing them,
Size is a good indicator, as you can’t grow to be six feet tall if you’re not well nourished and healthy. Muscles are also a good indicator, as is athleticism, for the same reason.
That is why women tend to find a sense of humor sexy. Not only is it fun to be around funny people, but a good sense of humor requires an agile mind to draw connections that other people find funny.
Facial symmetry is also an honest indicator of quality, as humans have evolved to be symmetric, but illnesses and accidents can disrupt that symmetry. Symmetry is a signal of health and genetic robustness
Sexual selection and mate competition are the driving forces behind the power of relativity, that is, the importance of our relative standing compared to others.
Experiments such as this one provide compelling evidence that once your survival needs are met, everything else is relative.
The sad truth is that the logic of sexual selection ensures that life remains a zero-sum game even when it doesn’t need to be.
Of all the preferences that evolution gave us, I suspect the desire to share the contents of our minds played the single most important role in elevating us to the top of the food chain.
If you drop one of us naked and alone into the wilderness, you’ve just fed the creatures of the local forest. But if you drop one hundred of us naked into the wilderness, you’ve introduced a new top predator to this unfortunate stretch of woods.
Nothing is more important to us than our social connections because nothing was more critical for our ancestors’ survival and reproduction.
Knowing others’ thoughts helps us fit in and predict what our group members will do next.
We also want our group to know our thoughts and feelings, as planting our beliefs in the minds of others provides the best opportunity for nudging the group in our preferred direction.
For these reasons, evolution has given us a perpetual desire to share the contents of our minds, even when there is nothing to gain at the moment by doing so.
evolution has given us a perpetual desire to share the contents of our minds, even when there is nothing to gain at the moment by doing so.
For our group to deal effectively with a threat or opportunity, we must all perceive it the same way, and thus we have evolved to seek emotional consensus.
There are few experiences in life more frustrating than sharing an emotional story with someone who reacts with indifference or an emotion opposite to our own. If I’m outraged by my colleague’s rude behavior, I’m even more outraged when my wife thinks it’s no big deal or, worse yet, funny or justified.
This need to share emotional experience sits at the root of nearly all exaggeration. If I’m worried that you won’t be sufficiently impressed by the fish I caught, then the fish grows in the telling.
There are clearly many qualities that enable people to be socially successful, but the fact that what works in one situation often does not work in another suggests that behavioral flexibility may be the single most important attribute for skilled social functioning.
One way to envision self-control is to imagine that your brain is like a chariot. The horses are your impulses, and they reside primarily in a small set of regions that sit under your cortex, near the base of your brain, such as the nucleus accumbens and the amygdala. The horses pull you toward gratification of your desires: food, sex, aggression, whatever it may be. Some people have wild stallions pulling their chariot, and they struggle to resist the temptation to eat too much, drink too much, have affairs, or punch the annoying guy in the nose. Other people are pulled along by petting farm ponies, and for them, managing their impulses is comparatively easy.
The chariot driver, who sits in a piece of the frontal lobes called the lateral prefrontal cortex (LPFC), is the one who resists temptation by reining in or redirecting the horses when the time, location, or goal itself is inappropriate. The driver has a copilot, who sits above the horses in or about the anterior cingulate cortex (ACC), and whose job is to alert the driver whenever the horses appear to be heading in the wrong direction.
These findings showed us that people who had better self-control were able to respond in a more flexible and socially skilled manner.
These studies show that self-control plays an important role in social functioning, but it didn’t occur to me for quite some time that social demands are probably what led to the evolution of self-control in the first place.
Most psychologists have taken it for granted that we evolved the capacity for self-control in order to pursue long-term goals. To be a successful farmer we must plant the seed rather than eat it; to have a happy retirement we must save our money rather than spend it; to maintain a healthy body weight we must decline the second piece of chocolate cake rather than eat it. But our world looks nothing like the world of our hunter-gatherer ancestors, who didn’t plant seeds or save money and who never worried about eating or drinking too much. Our ancestors were focused on today, with occasional thoughts of what they’d like to do tomorrow, so their lives were not the perpetual exercise in delayed gratification that ours have become.
First Boysen taught the chimps the numerals for one through nine. She then taught them to play a game that involved choosing the number of treats they would like to receive. In the game, two chimps are seated across from each other as in Figure 5.1a, and one chimp—we’ll call this one the chooser—has the opportunity to decide how many treats each will receive. The chooser is shown numbers on two separate cards, and its task is to point to one of the two numbers. The trick to this game is that the other chimp receives the number of treats shown on the card the chooser chimp points to, and the chooser receives the number of treats indicated on the other card. Chimps are not good at sharing, so their goal is always to get the larger pile for themselves and have the smaller pile go to the other chim