We also need brains that learn by reliably copying one another in order to establish laws and norms to live in harmony. We teach these norms to our children as we wire their little brains to their world. We teach them to newcomers, not only to smooth day-to-day interactions but also to help the newcomers survive. I’ve read about explorers in the 1800s who ventured into inhospitable, uncharted parts of the world, where many of them died. The expeditions that survived were the ones whose members became acquainted with the indigenous people in those regions; they taught the explorers what to eat, how to prepare the food, what to wear, and other secrets of survival in the unfamiliar climate. If all individual humans had to figure out everything themselves without copying, our species would be extinct.
We need brains that cooperate on a vast geographical scale. Even the most mundane act, like reaching into a kitchen cupboard for a can of beans, is possible only because of other humans. Other humans planted and watered those beans, perhaps thousands of miles away. Other humans mined the metal for the can. Still other humans transported the beans to your local store, which was built by other humans with wood and nails and bricks that were manufactured and hauled by other humans, using techniques and tools invented by other humans long dead. You paid for the beans with money that was invented and blessed by a government of other humans. Thanks to a shared social reality, all these thousands of people were in the right place at the right time doing the right things for you to grab the can and make dinner.
Creativity, communication, copying, and cooperation—four of the five Cs—arose with genetic changes that gave our species a big, complex brain. But large brain size and high complexity are not enough to make and maintain social reality. You also need the fifth C, compression, an intricate ability that humans have to a degree not found in any other animal brain. I’ll explain compression first by analogy.
Imagine that you are a police detective investigating a crime by interviewing witnesses. You hear one witness’s story, then another’s, and so on, until you’ve interviewed twenty witnesses. Some of the stories have similarities—the same people involved or the same crime location. Some stories also have differences—who was at fault or what color the getaway car was. From this collection of stories, you can trim down the repetitive parts to create a summary of how the events might have occurred. Later, when the police chief asks you what happened, you can relay that summary efficiently.
A similar thing transpires among neurons in your brain. You might have a single, large neuron (the detective) receiving signals from umpteen little neurons at once (the witnesses) which are firing at various rates. The large neuron doesn’t represent all of the signals from the smaller neurons. It summarizes them, or compresses them, by reducing redundancy. After compression, the large neuron can efficiently pass that summary to other neurons.
This neural process of compression runs at a massive scale throughout your brain. In your cerebral cortex, compression begins with small neurons that carry sense data from your eyes, ears, and other sense organs. Some of this data may already have been predicted by your brain, and some is new. The new sense data is passed by the small neurons to larger, better-connected neurons, which compress the data into summaries. Those summaries are passed to still larger, more highly connected neurons, which compress those summaries and pass them on to even larger, even more highly connected neurons. The process continues all the way to the densely wired front of your brain, where the very largest, most connected neurons create the most general, most compressed summaries of all.
Compression in the brain, which enables abstraction (this diagram is conceptual, not anatomically precise)
Okay, your brain can make a big, fat, compressed summary of summaries of summaries. What does this have to do with social reality? Well, compression makes it possible for your brain to think abstractly, and abstraction, together with the rest of the Five Cs, empowers your large, complex brain to create social reality.
Usually when people talk about abstraction, they mean something like abstract art, how you can look at a painting by Picasso and see a face in the cubes. Or they mean abstract math, like using algebra to rotate an object on its axes. Or they mean abstract symbols, like using a squiggle of ink on paper to represent a number, and a column of numbers to represent your spending for the month.
The psychological meaning of abstraction, though, has a different focus. It’s not about the details of paintings and symbols; it’s about our ability to perceive meaning in them. Specifically, we have the capacity to see things in terms of their function, not just their physical form. Abstraction lets you view objects that look nothing alike—such as a bottle of wine, a bouquet of flowers, and a gold wristwatch—and understand them all as “gifts that celebrate an achievement.” Your brain compresses away the physical differences of these objects and in the process, you understand that they have a similar function.
Abstraction also allows you to impose multiple functions on the same physical object. A cup of wine means one thing when your friends shout, “Congratulations!” and another when a priest intones, “Blood of Christ.”
Here’s how abstraction works. As your brain compresses data from all your senses, it integrates them into a cohesive whole, an activity that we previously called sensory integration. Each time one of your neurons compresses its inputs to make a summary, that multisensory summary is an abstraction of the inputs. At the front of your brain, the largest, most highly connected neurons produce your most abstract, multisensory summaries. That’s why you can view dissimilar objects like flowers and gold watches as similar and view an identical cup of wine as either celebratory or sacred.
I wrote in lesson no. 2 that you have a highly complex brain but high complexity isn’t enough to make a human mind. Complexity may help you climb an unfamiliar staircase, but you need more to understand the idea of climbing a social ladder to gain power and influence. Abstraction is another necessary ingredient. It lets your brain summarize bits of past experience to understand that physically different things can be similar in other ways. Abstraction gives you the power to recognize things you’ve never encountered before, such as a woman with snakes for hair. You’ve probably never seen a real one, but you (and the ancient Greeks) could look at a picture of Medusa and instantly comprehend what she is, because, miraculously, your brain can assemble familiar ideas like woman and wild hair and slithering snake and danger into a coherent mental image. Abstraction also lets your brain assemble sounds into words, and words into ideas, so you can learn language.
In short: The wiring of your cerebral cortex makes compression possible. Compression enables sensory integration. Sensory integration enables abstraction. Abstraction permits your highly complex brain to issue flexible predictions based on the functions of things rather than on their physical form. That is creativity. And you can share these predictions by way of communication, cooperation, and copying. That is how the Five Cs empower a human brain to create and share social reality.
Each of the Five Cs is found in other animals to varying extents. Crows, for example, are creative problem-solvers who use twigs as tools. Elephants communicate in low rumbles that can travel for miles. Whales copy one another’s songs. Ants cooperate to find food and defend their nest. Bees use abstraction as they wiggle their bums to tell their hive-mates where to find nectar.
In humans, however, the Five Cs intertwine and reinforce one another, which lets us take things to a whole other level. Songbirds learn their songs from adult tutors. Humans learn not only how to sing but also the social reality of singing, such as which songs are appropriate on holidays. Meerkats teach their offspring to kill by bringing them half-dead prey to practice on. We learn not only about killing but also the difference between accidental killing and murder, and we invent different legal penalties for each. Rats teach one another what’s safe to eat by marking palatable foods with an odor. We learn not only what to eat but also which foods are main courses versus
desserts in our culture and which utensils to use.
Other animals, such as dogs, great apes, and certain birds, also have brains that compress signals to a degree, so they can also understand things abstractly to some extent. But as far as we know, humans are the only animal whose brains have enough capacity for compression and abstraction to create social reality. A single dog might develop its own social rules, like that a particular grassy area is for playing with humans or that pooping is not allowed inside the house. But a dog brain cannot communicate these concepts to other dog brains efficiently the way human brains convey concepts with words to make social reality. Chimps can observe and copy one another’s practices, like poking a stick into termite holes to pull out tasty snacks, but this learning is based in physical reality—namely, that sticks fit into termite holes. That’s not social reality. If a troop of chimps agreed that whosoever pulls a particular stick out of the ground becomes king of the jungle, that would be social reality, because it imposes a sovereign function on the stick that goes beyond the physical.
Most animals have evolutionary adaptations that make them specialists in their niches, like an elk’s antlers or an anteater’s tongue. But humans became generalists; evolution blended the Five Cs into a potion that spurs us to bend the world to our will. All animal brains pay attention to things in their physical environment that are relevant to their well-being and survival and ignore the other stuff. But humans don’t just select stuff from the physical world to create our niche. We add to the world by collectively imposing new functions, and we live by them. Social reality is human niche construction.
Social reality is an incredible gift. You can simply make stuff up, like a meme or a tradition or a law, and if other people treat it as real, it becomes real. Our social world is a buffer we build around the physical world. The author Lynda Barry writes, “We don’t create a fantasy world to escape reality. We create it to be able to stay.”
Social reality can also be a huge liability. It’s so powerful that it can alter the speed and course of our genetic evolution. One example is the tragedy of the Romanian orphanages, when a government’s rules created a generation of humans who were effectively removed from the gene pool. Another example is China’s one-child policy, which, in a culture that values sons over daughters, led to more male offspring than female and ultimately to millions of Chinese men who cannot marry Chinese women. This sort of artificial selection happens in every society where wealth, social class, or war empowers one group over another—it changes the odds that certain people will reproduce with each other, or at all. Social reality even changes the course of human evolution when we simply share our creative ideas, such as the technology to burn fossil fuels, which has produced a physical world that is less under our control.
A really striking thing about social reality is that we often don’t realize that we make it. The human brain misunderstands itself and mistakes social reality for physical reality, which can cause all sorts of problems. For example, humans vary tremendously, like every animal species does. But unlike the rest of the animal kingdom, we organize some of this variation into little boxes with labels such as race, gender, and nationality. We treat the labeled boxes as if they’re part of nature when in fact we build them. Here’s what I mean. The concept of “race” often includes physical characteristics such as skin tone. But skin tone is on a continuum, and boundaries between one set of shades and another are placed and maintained by people in a society. Some try to justify the boundaries by appealing to genetics, but while it’s true that skin tone might be heavily influenced by genes, so are eye color, ear size, and the curvature of toenails. We, as a culture, choose the features of discrimination and draw dividing lines that magnify the differences between the group we call “us” and the group we call “them.” The lines aren’t random, but they aren’t stipulated by biology either. And after the lines are drawn, people treat skin tone as a symbol for something else. That is social reality.
You uphold social reality by your everyday behaviors. You do it every time you treat sparkling diamonds like they have value, every time you idolize a celebrity, every time you vote in an election, and every time you don’t vote in an election. Our behaviors can also change social reality. Sometimes the changes are relatively small, like using the pronoun they to refer to a single person instead of a group. Other times the changes are cataclysmic, like the breakup of the former country of Yugoslavia, which led to years of war and genocide, or the Great Recession of 2007, when some people in fancy suits decided that a bunch of mortgages had dropped in value, and so they did drop, plunging the world into catastrophe.
Social reality does have its limits; after all, it’s constrained by physical reality. We could all agree that flapping our arms will let us soar into the air, but that won’t make it happen. Even so, social reality is more malleable than you might think. People could agree that dinosaurs never existed, ignore all evidence to the contrary, and build a museum about a dinosaur-free past. We could have a leader who says terrible things, all captured on video, and then news outlets could agree that the words were never said. That’s what happens in a totalitarian society. Social reality may be one of our greatest achievements but it’s also a weapon we can wield against each other. It is vulnerable to being manipulated. Democracy itself is social reality.
Social reality is a superpower that emerges from an ensemble of human brains. It gives us the possibility to chart our own destiny and even influence the evolution of our species. We can make up abstract concepts, share them, weave them into a reality, and conquer just about any environment—natural, political, or social—as long as we work together. We have more control over reality than we might think. We also have more responsibility for reality than we might realize.
Every type of social reality is a dividing line. Some dividing lines help people, such as driving laws that prevent head-on collisions. Other dividing lines benefit some people and hurt others, such as slavery and social class. People debate the morality of such dividing lines, but like it or not, each of us bears some responsibility every time we reinforce them. A superpower works best when you know you have it.
Epilogue
ONCE UPON A TIME, you were a little stomach on a stick, floating in the sea. Little by little, you evolved. You grew sensory systems and learned that you were part of a bigger world. You grew bodily systems to navigate that world efficiently. And you grew a brain that ran a budget for your body. You learned to live in groups with all the other little brains-in-bodies. You crawled out of the water and onto land. And across the expanse of evolutionary time—with the innovation that comes from trial and error and the deaths of trillions of animals—you ended up with a human brain. A brain that can do so many impressive things but at the same time severely misunderstands itself.
A brain that constructs such rich mental experiences that we feel like emotion and reason wrestle inside us
A brain that’s so complex that we describe it by metaphors and mistake them for knowledge
A brain that’s so skilled at rewiring itself that we think we’re born with all sorts of things that we actually learn
A brain that’s so effective at hallucinating that we believe we see the world objectively, and so fast at predicting that we mistake our movements for reactions
A brain that regulates other brains so invisibly that we presume we’re independent of each other
A brain that creates so many kinds of minds that we assume there’s a single human nature to explain them all
A brain that’s so good at believing its own inventions that we mistake social reality for the natural world
We know much about the brain today, but there are still so many more lessons to learn. For now, at least, we’ve learned enough to sketch our brain’s fantastical evolutionary journey and consider the implications for some of the most central and challenging aspects of our lives.
Our kind of brain isn’t the biggest in the
animal kingdom, and it’s not the best in any objective sense. But it’s ours. It’s the source of our strengths and our foibles. It gives us our capacity to build civilizations and our capacity to tear down each other. It makes us simply, imperfectly, gloriously human.
Acknowledgments
This book owes its existence to many people, particularly the neuroscientists who educated me in their craft, guided my reading, and patiently answered my unending questions with unwavering generosity and good cheer. First and foremost is the incomparable Barbara Finlay. Barb is a connoisseur of evolutionary and developmental neuroscience. She regularly astounds me with her encyclopedic knowledge as she instructs me in the finer points of embryology and continually exposes me to a smorgasbord of neuroanatomy and neuroscience topics from the perspective of evolution and development. The half-lesson and lesson no. 1 in this book would not exist without Barb, and her fingerprints can be found in other lessons. Barb and I are currently collaborating on an academic book on the evolution and development of motivation and emotion in vertebrates, to be published by MIT Press.
I am also exceedingly grateful to my longtime collaborator and friend, neurologist Brad Dickerson. We’ve collaborated on brain-imaging studies for more than a decade at Massachusetts General Hospital in Boston, and we’ve published more than thirty research papers together. I particularly appreciate his willingness to indulge my sometimes exuberant scientific speculations. Special thanks also to Michael Numan, who was the first neuroscientist to encourage and support me as I began my neuroscience education.
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