9781785045271 by Smakprov Media AB

NATURE AND THE MIND

The Science of How Nature

Improves Brain, Body and Community

DR MARC G. BERMAN

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To my grandparents, whose lives and experiences inspired me to study the mind, and to my parents, kids, and Katie, who have continued to support me on this journey. And to Steve, who inspired me to work in this area in the rst place.

PREFACE

This is a book about the founding of a whole new field of scientific inquiry, one that describes the relationship between nature and the mind.

Where shall we begin?

We could start in 2012, when I coined the term environmental neuroscience to describe our new field. And we’ll get there.

We could go back further, to my first memories of interacting with trees—and we’ll get there, too.

But when I tell the story, I like to start with one study.

Before that study, my path was unclear.

After that study, the future became inevitable.

I say “the future” here, and not just my future, because while this study changed my life, I think it will change yours, too.

We called this study “A Walk in the Park,” but designing it, even asking the questions that led to it, was far from easy. It took generations of theorizing on human nature and what environmental psychologists—of which I am one—call the human-nature connection.

Though this study was far from easy, it seemed on its surface simple.

We asked a group of volunteers to complete cognitive tasks designed to challenge their memory and attention, and then we sent them on a walk.

For example, participants would hear digits out loud, like 4 - 97 - 5 - 1, and then would need to repeat them back in backwards order: 1 - 5 - 7 - 9 - 4. This is called the backwards digit span task, and it challenges participants’ memory and attention. It is a hard task, and during the study we kept increasing the number of digits, up to nine.

Half the participants then went on a walk through nature, leaving the

University of Michigan and strolling through the Ann Arbor Arboretum, then following a winding path down to the Huron River, passing the evergreens as they followed the trail. The other half walked for the same distance and the same amount of time, but followed a route through a busy urban part of Ann Arbor along a four-lane street where cars whizzed by. They had to navigate intersections and walk along a commercial street, with its storefronts and typical downtown atmosphere.

When our volunteers got back to the lab, we retested them on the same memory and attention tasks, including the diﬃcult backwards digit span task.

To have more control over the experiment, and to make sure there was nothing unbalanced in our groups, we repeated the whole procedure again a week later, switching which route we assigned to each person. So, a participant who walked through a busy urban area the first week then walked in nature the next week, or vice versa.

Our findings were breathtaking and decisive: Our volunteers’ performance on the memory and attention tasks greatly improved following their walk in nature, but didn’t improve after a walk through a busy urban area.

Other studies had asked people how they felt after time in nature, but none had ever quantified nature’s impact on our cognition using objective measures.

We published what we’d discovered in a prestigious psychology journal, where our paper became one of its most cited articles in that journal’s history. Soon, reporters from all over the world began contacting me. They saw what we had: We were on to something. Back then, I could never have imagined what happened next. But now, I can see clearly that everything I’d experienced and everything I’d studied until this particular experiment had, in its way, prepared me for this moment—and prepared me to found the field of environmental neuroscience.

This book is a detailed account of this new field and its revolutionary findings, which show that the unique sensory experience of the natural world improves our cognitive, physical, social, and emotional well-being. It is also a story of how this new field came to be, and where I hope it will go next.

Introduction

The Foundations of Environmental Neuroscience

We can never have enough of nature. We must be refreshed by the sight of inexhaustible vigor, vast and titanic features, the seacoast with its wrecks, the wilderness with its living and its decaying trees, the thunder-cloud, and the rain which lasts three weeks and produces freshets. We need to witness our own limits transgressed, and some life pasturing freely where we never wander.

—Henry David

Thoreau, naturalist, essayist, poet, and philosopher, Walden

This is a book about why nature matters so much to us, and how our interactions with nature can tell us more about our own psychology— and even how our brains work. I’ve spent my career as an environmental neuroscientist running experiments to understand the human-nature connection, but I didn’t always feel that nature was all that important. I grew up an anxious suburban kid.

During the summers, my parents sent me packing from our home in Detroit to stay with my grandmother at her place in the woods of Michigan. There, I often hid in the trunk of the old blue spruce tree on my grandmother’s land. I liked running my fingers across the rough bark of the branches and the soft prickles of the pine needles. Bugs I didn’t know the

names of crawled along the trunk. From my secret refuge, I could hear my cousin’s voice: ten . . . nine . . . eight . . . Soon, she’d come looking for me. I could hear the birds above me, my cousin’s muﬄed laughter, the screen door slam as Grandma Ruth came out of the house to watch us play among those trees she’d planted so many years before.

I want to tell you about how my grandparents came to this special place, and planted these special trees, because it was a decision that changed their lives, and my parents’, and mine, and led to the insights I’ll share in this book. My grandmother’s decision to plant the blue spruce trees is a reflection of our ongoing, complicated, rich, marvelous relationship with nature.

Ruth Eleanor Nelson, my maternal grandmother, was a hard woman from the Upper Peninsula of Michigan. She had icy blue eyes and a nose mysteriously without cartilage. She hated snakes, but if she saw one, she wouldn’t shriek; she’d just chop it in half with the blade of a shovel. She never wore skirts or dresses, not even for special occasions. My cousins thought she was tough, maybe a little mean, but I always thought she was sweet. “Here comes Glamor Boy,” she’d say as I approached—the city kid. My mom, Sharon, met my dad, Sidney, in college at the University of Michigan. They were from somewhat diﬀerent worlds—my mom growing up Lutheran in a more rural environment, and my dad growing up Jewish in a more suburban environment. They shared a love of knowledge and education, as well as strong beliefs about right and wrong.

My parents named me after my maternal grandfather, Merl Glenn Swann. My parents didn’t want to name me Merl, so they replaced it with Marc, but kept his middle name fully intact, Glenn. Unfortunately, Grandpa Merl died young, long before I was born. Even though I never knew him, he lived in my imagination. He had the nickname “the Deer” because he ran so fast and gracefully on the football field, where he was a star running back for Grand Rapids South (the same high school and football team that former president Gerald Ford had played for a few years earlier). I remember seeing pictures of him in his football uniform from his yearbook and also from newspaper clippings of his triumphs on the football field. He was small, only five foot eight and maybe 135 pounds, which is why he said he

had to run so fast. I also remember hearing how he got his two front teeth knocked out trying to block a punt, a reminder of how brutal the game was, especially in those days with such minimal padding and no face masks. He wore number 21, which became my mom’s favorite number and then mine (the same number as the diminutive but great Michigan football player Desmond Howard, my favorite player). He was also a great baseball player and class president. He seemed like someone who was good at everything.

I also remember seeing him in his army uniform and hearing stories of how he had failed his first physical to be in the army because he had been out drinking too much the night before. This delighted his mother, but he returned to enlist a few days later and passed with flying colors. His younger brother Don, not to be left behind, enlisted in the Marines at age sixteen. I remember hearing how my grandfather admired General Douglas MacArthur, who remembered everyone’s name that he met. My grandpa earned a Bronze Star in World War II, though we don’t know the specifics as he didn’t talk about it, and unfortunately his records burned in a fire at a military archives facility in Kansas City.

I knew my grandpa was a hero.

Sometimes, I fantasized that Grandpa Merl had been sent to liberate the concentration camps at Auschwitz, Gross-Rosen, and Buchenwald, where my paternal grandpa had suﬀered, or the bomb-making factory where my paternal grandmother and her sister were forced to work—doing whatever they could so that the bombs might fail. I could almost see the beautiful symmetry of it: One grandparent rescuing two others, ensuring the possibility of my parents’ birth—and of my birth. A lineage of care from chaos.

Of course, this was a childhood fantasy. My grandpa Merl was fighting in the Pacific while my dad’s parents were suﬀering in Europe. But it was a nice fantasy, one that I still smile about now.

Years after my grandpa Merl got back from the war, he bought this land with my grandma Ruth. They intended to start a small farm together. Not as a profession, but as a way to connect to the land. They had a barn with a horse and cow, and they grew tomatoes, green beans, cabbage, rhubarb, corn, cauliflower, watermelons, and pumpkins. I remember as a kid

gnawing on the rhubarb. At the end of a long driveway, oﬀ a long dirt road, they built a house, and across the driveway they planted the stand of five blue spruce trees. The blue spruce, to my grandmother’s eye, was a fancy tree, a small investment in her landscape. She bought them as saplings, but not penny saplings. These were taller when they went into the ground; they were more established. They rooted quickly.

My mom moved away to raise my sister and me in the suburbs of Detroit, where my dad got a job and where all my dad’s family lived—my aunts, my uncles, and my grandparents. My mother’s siblings stayed close by, and so all seven of my cousins grew up among these trees.

I loved visiting Grandma Ruth and her land, but I was an outsider there. Unlike my cousins, I didn’t know the names of the animals or their sounds. I was afraid of the darkness that descended when night came, a darkness so deep that it seemed to have no end. When I was bored, I preferred to watch cartoons on TV, not go for a walk. Then there was the fact that I felt diﬀerent from the other people in town, and even a bit diﬀerent from my cousins. It wasn’t obvious, but I had a slightly darker complexion compared to many of the more blond and fair-skinned people who lived nearby, many of whom had Dutch ancestry like some of my cousins. I knew that my parents, my sister, and I were the only Jewish people around.

At the same time, it didn’t really matter that I was diﬀerent from others in my family. I, too, felt bound to this land. By the time I knew these blue spruce trees, they had grown tall and wide, with hollows beneath where the land gave way to a hill. I could crawl up under the low branches, which would scratch at my arms and knees, and nestle inside the tree—the rough bark, the birds overhead, the needles crisscrossing around me—listening for the countdown to end the game of hide-andseek so I could be found.

By the time my grandmother left her farm, the trees had grown so big they hid the front of her house. My mother knew she wanted to save a piece of that place. She couldn’t take one of the established blue spruce— they were far, far too big—but she’d helped plant more alongside the house in the years since my grandmother first moved in. On her last visit, she

went looking for a sapling—one that was established enough to withstand a move, but young enough to be uprooted. When she found it, she began to dig. She lifted it from the earth and put it into a plastic bucket.

I remember thinking it looked pathetic there, like a Charlie Brown Christmas tree. I wondered if my mom was out of her mind. The tree rode with us in the back seat of the car, nestled between my sister’s and my feet, all the way back to Detroit.

Back home, my mother acted quickly, digging a hole in the corner of our yard and placing the sapling in the ground. I thought for sure it wouldn’t survive, but she had seen the first five spruces blossom into giants. My mother had vision; she had faith. She knew a tree could thrive. Maybe on some level she knew this, too: It would help us all thrive.

Over the years, that sapling did eventually grow into a giant. I would take shelter in the trunk, look out at the repeating patterns of the pine needles, mesmerized by their gradations of color. At the time, to me, they were just trees; I didn’t think much about them or what they might be doing to my brain.

Philosophers and popular thinkers had spent millennia thinking about nature and waxing poetic about its restorative power, and for a long time, that seemed convincing enough. Paradoxically, the more human existence was concentrated in cities, the more widely agreed upon it became that access to nature was “good” for us. Go to the country to convalesce, people said. Take a vacation at sea. “There is something infinitely healing in the repeated refrains of nature,” twentieth-century biologist Rachel Carson wrote. “The splendor of cherry blossoms dwells in my heart,” the fifteenth-century Japanese poet Matsuo Bashō wrote when his nephew was dying of tuberculosis, “and thinking this the sick person’s final blossom season, I took him to see them, and he was joyful.” In many religions, heaven is the Garden of Eden, and books like e Secret Garden by Frances Hodgson Burnett describe interacting with nature as a way to heal people. Still, for all this accepted wisdom, until I launched the Environmental Neuroscience Lab at the University of Chicago, few scientists had ever studied the eﬀects of nature on our brains.

That’s because most neuroscientists focus inwards, trying to understand what happens inside the human brain and how it produces our behavior and cognitive functions. On the other hand, most environmental scientists focus outwards, on what’s going on in the world around us. Bringing the two together, I came to realize how fundamentally our surroundings shape us, and I began to wonder if nature might even hold the antidote to many of the things that ail us today.

I felt compelled to help and founded the new hybrid field of environmental neuroscience. Unlike my cousins who stayed in rural Michigan, most of the time I spend looking at trees and other elements of the natural world I’m doing it from a lab in Chicago, looking at the human brain and observing human behavior as it responds to nature.

I focus on the habits and abilities that emerge in people when they touch the soft leaves of a sage plant, hear the call of a goldfinch or the crashing of ocean waves, smell wet soil or fresh roses, or watch a candycolored sunset over the Grand Canyon. With my team, I examine functional magnetic resonance imaging (fMRI) scans from MRI machines that measure blood oxygenation levels and can tell us what brain areas are active when people are doing different tasks, seeing different stimuli, or thinking different thoughts. We immerse participants in real and virtual nature environments and see if they perform better on attention and memory tasks—like the backwards digit span task—after they interact with natural environments versus more urban environments. We work with an eye tracker to collect data on eye movements (a measure of where people are attending) to see if people move their eyes differently when looking at pictures of more natural scenes versus more urban scenes. We use cell-phone tracing data from hundreds of thousands of people to quantify how often people in different neighborhoods visit parks and whether neighborhoods that have residents who visit parks more often have less crime. And that’s just the start.

As an environmental neuroscientist, I get to study the external environment and the internal biological and psychological human processes in concert to explore important questions. Such as: How does the natural

world impact us psychologically? In what ways is environmental destruction aﬀecting our brains? How could we alter the environment to improve our well-being? Can we use our discoveries about the interactions between nature and human biology to design better environments?

The answers to these questions reveal that our relationship with our environments is more interconnected and more complex than science has ever before considered. A simple walk in nature leads to startling increases in our memory and focus. Some studies have found that we can get similar—although less dramatic—eﬀects by looking at pictures of nature, whether a photograph of a great hemlock tree or videos of waterfalls, or just by listening to birds sing. Nature lovers will nod with intuitive understanding to these findings, but we’ve discovered that people don’t even need to like nature to get these cognitive benefits. Nature is beneficial like the vegetables we know are good for us, whether or not we find them tasty.

I’m not the first person to extol the benefits of contact with nature, but this isn’t just another nature book—it’s a book about previously unknown fundamentals of human biology and psychology and how nature impacts them. Because it turns out that the way nature interacts with our brains and bodies improves our cognition, helps us process grief and manage depression and anxiety, and, perhaps most profoundly, can provide hope for the millions of us who struggle with attention and focus in today’s busy world, because nature has a unique power to restore our ability to focus. It turns out that our ability to focus is hugely crucial to our lives; not just to keep us productive but to exert self-control. We don’t have to throw away our smartphones, sell our houses, or vanish into the woods. Just a short stroll, a well-placed houseplant, or a brief listen to birdsong can have profound impacts on our health and well-being. Again, you don’t even need to like nature—you just need to welcome it into your life.

For all of us who sometimes feel drained, distracted, isolated, or depressed, I have identified the elements of a “nature prescription” that can inspire happiness and hope, renew energy and attention, and spur cooperation and connection. The evidence-backed results apply at work or at home,

indoors or out, alone or with colleagues, friends, or family—and don’t require moving out of cities or sacrificing modern existence.

We’ll talk at length about all of these things later in this book, but to give you a preview of the breadth of our discoveries, know that just living on a street with more trees is related to better health. In my lab, we’ve found that having eleven more trees per city block is related to a 1 percent decrease in cardio-metabolic conditions like stroke, diabetes, and heart disease.1 That may not sound dramatic at first, but to get that equivalent health boost with money or youth, you’d need to give everyone in the neighborhood around twenty thousand dollars or magically turn the aging clock back by almost a year and a half. Perhaps even more surprising, we’ve shown that even fake plants in our environments can deliver health benefits, so I’ve added them to my out-of-town oﬃce where I can’t water live plants regularly. As we’ve focused on our investigations, we’ve discovered that even a view of a tree or the sound of birdsong can impact everything from school performance to crime rates to how fast we recover from surgery.

All this to say, nature isn’t an amenity—it’s a necessity.

Throughout this book, I’ll tell you stories from my own life and research. My career has taken me to many diﬀerent cities. After I left home in the suburbs of Detroit, I went to school at the University of Michigan in Ann Arbor for both undergraduate and graduate studies. Since earning my doctorate, I spent a few years in Toronto, Canada, as a postdoc, was a professor at the University of South Carolina, and am now a professor at the University of Chicago, but I split my time between the Windy City and Toronto. Since environment is so important to this book, I mention each city as the backdrop to the stories I mention above.

Whatever city or place I find myself in, I make my work and family life a laboratory for the human-nature connection. I work, plan, and make major decisions diﬀerently now. I’ve shifted how I equip my home and office, the places I play and pray, what I watch and listen to to relax, and even the designs I choose for walls, windows, and doors. My university lab is in a busy city, my daily life can be quite stressful, but, using nature, I now know where to go and what to do to recharge, reduce mental fatigue, find focus,

boost creativity, deepen my relationships, lift depression, or ponder the future. I even owe my marriage to this work—and my wife and I apply many of our findings to how we raise our four young children. Environmental neuroscience has led me to grand visions of saving society with a worldwide nature revolution, but like every vast transformation, this one can start very small, with each of us: Just add a little green and experience the benefit in action. As you read these pages, I invite you to make your own life a laboratory for the nature revolution. And one of the first elements we’ll consider is something you may not immediately associate with the natural world: the current crisis in human attention. Because just as nature is more interconnected with the human mind than science has ever previously understood, human attention is the surprising root system of all that our minds do—it’s the common resource that our cognitive, physical, social, and emotional health depends on.

To be without trees would, in the most literal way, to be without our roots.

—Richard Mabey, nature writer, author, and journalist

— PART ONE — HOW THE ATTENTION CRISIS

IS AT THE ROOT OF OUR INQUIRY

Chapter 1 Human Nature

At many points along the way these various studies did not seem particularly related, but gradually, from these separate parts, a coherent sense of the whole has begun to emerge.

—Rachel Kaplan and Stephen Kaplan, environmental psychologists, The Experience of Nature

Iwas a teenager when I first read Isaac Asimov’s Foundation series. Set in the year 12,067 of the Galactic Era, a mathematician named Hari Seldon establishes a new field of science that can actually predict the future. As an anxious kid, I imagined this could solve my problems. Seldon’s field, called psychohistory, combined history, physics, math, sociology, and psychology. I put the book down and gazed out the window at my suburban Detroit neighborhood, imagining a world where I could be a psychohistorian, using my love of math and science to analyze the past and create vast equations to forecast the future with calm certainty. I sighed. I knew there probably wasn’t any major like that at the University of Michigan. The truth was, I didn’t know what I wanted to do or “be” when I grew up. Psychology sounded interesting, but I didn’t see myself becoming a therapist. I was the famously nervous one in our family. My father used to scold me: “Marc, you spend four hours worrying about your homework and one hour doing it.” That was true.

Despite the several times a year I was let loose to wander around my grandmother’s farm, I lived my mostly suburban life afraid of a world I knew to be inherently dangerous. My grandpa Merl’s early death stayed with me, and I hated going to school because I worried my parents would die when they were out of my sight. Nothing drove my ambiguous fear more than the knowledge that my paternal grandparents had survived the Holocaust. There was never a time I didn’t know they were Holocaust survivors—or at least none that I remember—but until fifth grade, I wasn’t privy to any of the details. I knew that we’d lost several family members, but I didn’t know how or how many. My grandparents never told their children what had happened to their parents, to their siblings, or even to themselves. Maybe it was too close, too painful; maybe they didn’t think their children could endure that story. But when I was in fifth grade, my grandpa Ludwig began to open up to me. It happened mostly on Shabbat—Saturdays—after services. We’d all go back to my grandparents’ home, where my grandma Ella had prepared an amazing meal of cholent, a traditional Jewish stew (she made it vegetarian), along with noodle kugel and blintzes. We ate together as a family, but after lunch, everyone scattered, leaving me and my grandfather at the kitchen table alone. It was there that I began to ask him questions, and he answered. The letter and numbers tattooed on his left arm took on a new weight. I began to reckon not only with abstract danger, but with the violent acts of individual people.

Often my grandfather’s stories were those of small miracles and near misses. There was the story of the time he lied and said he was a mechanic, which got him out of Auschwitz, where he never would have survived very long. Or the time a German soldier threw him from a shower into a pit of refuse—shit and piss and who knows what else—where he nearly drowned until someone saw his hand above the surface and pulled him out. I learned that at the end of the war he weighed only ninety pounds, and when the US soldiers found him, he was in a coma. They thought he was a corpse and piled his body with the dead. It was only when one soldier saw a toe twitch that he realized my grandfather was alive, pulled his body from the pile, and brought him to a hospital. The simple fact that my grandfather would have died if that soldier hadn’t noticed my grandfather twitch haunted me.

It was important to me to receive these stories, to know this history, and to know my grandpa Ludwig in this way. But the stories lodged deep. In seventh-grade Hebrew school, we were supposed to interview a Holocaust survivor and do a presentation about their experiences. I chose my grandfather. When it was my turn to present, I went to the front of the classroom, made it through the first three sentences of my presentation, and then started to cry. I couldn’t recover the moment. I cried until I went back to my seat. The weight of it was too heavy. Others had interviewed family friends, or friends of friends, but for me it was too close to home. This evil was done to my grandparents.

I couldn’t wrap my head around how it could happen, how people like Nazis could exist. I wanted to know what went so wrong that this kind of suﬀering could be wrought. I obsessed over how people could be so evil. Were they just born that way?

I got nervous at sleepovers—even at my grandparents’ houses.

My little sister shook her head and tried to explain it to our cousins: “My big brother just misses his mama.”

In other words, I wasn’t exactly the calm, healing personality you’d want in a therapist.

My dad practiced law and warned me, “Just don’t become a lawyer, Marc, it’s too stressful.”

My mom was a nurse. She sighed into her morning coﬀee and shook her head. “Whatever you do, Marc, don’t go into medicine.”

“Bob seems happy,” my father oﬀered, peering out from behind his newspaper. “He’s an engineer.”

My mom agreed. “My friend Kay likes her job, too.”

So it was, for lack of a better idea, that I started at the University of Michigan intending to become a computer engineer. I was good enough at the various aspects of understanding hardware and writing software, but it didn’t come naturally to me. I had to cram to keep up with the other students. I didn’t enjoy sitting in front of a computer all day long, and I’d find my attention waning before my assignments were done. Worse still, I noticed that I didn’t really care about making computers faster or more

eﬃcient. I often felt that with each class, I almost knew less than I had before—because now there was a whole slew of new material that I’d need to study. My lack of passion depressed me. My dad used to say to try to find something that scratches an itch, and I just hadn’t found it yet. I thought about quitting school, but that made my anxiety kick in. What would I do if I dropped out? I remember taking some inspiration from the movie O ce Space and how the main character, Peter, after being hypnotized, starts to let go of all his anxieties about work and love and just chills out. I remember my mom being disappointed that I took inspiration from that movie, and I still smile about that.

But back to science. If I could predict the future like a psychohistorian, maybe I wouldn’t have worried so much. Instead, the years ahead loomed like shadows, scary and unknowable. I tell you this because both my anxiety and my time studying computer engineering would lead me to discover fundamental aspects of human nature, and how the environment can shape it. So, too, did an Intro to Psychology class.

PSYCH 101

As a freshman, I took lots of survey classes alongside my computer engineering requirements. There was, of course, one class that changed my whole perspective—and set me on the path to spend my life exploring the interactions between nature and the mind. In Intro to Psychology, taught by the famous psychologist Chris Peterson, a pioneer in positive psychology, I learned about the Milgram experiment, a 1961 study of human nature.1 Yale University psychologist Stanley Milgram wanted to understand why so many people participated in the horrors of the Holocaust, so he set out to measure how much pain one person would inflict on another if they were asked to do so by an authority figure. He did his experiment somewhat sneakily—and in many ways unethically. These days, you couldn’t run an experiment the way he did back then. The study participants, all male, were told they were part of a study looking at the relationship be-

tween punishment and learning. In truth, Milgram was interested in observing obedience to authority.

It’s a famous study you’ve probably heard of even if you’ve never taken Psych 101, but it was new to me. The experiment involved three players: a scientist (who was the experimenter), an actor who pretended to be a study participant, and the actual study participant. In the experiment, the two “participants” drew slips of paper to seemingly randomly choose who would be the learner and who would be the teacher. The slips both said teacher, but the actor claimed that his said learner.

Then the scientist/experimenter and the teacher—the teacher being the actual study participant—went into one room, while the learner, the actor, went into another. Before the experiment started, the teacher saw the learner being hooked up to what appeared to be a small electric chair, his arms strapped down, and an electrode attached to his wrist.

In front of the teacher was a shock generator, labeled from 15 to 450 volts. The learner was then asked to remember pairs of words. If he got them wrong, the teacher was instructed by the experimenter to administer increasingly severe shocks. “At 75 volts, [the learner] grunts,” Milgram wrote; “at 120 volts, he complains loudly; at 150, he demands to be released from the experiment. As the voltage increases, his protests become more vehement and emotional. At 285 volts, his response can be described only as an agonized scream. Soon thereafter, he makes no sound at all.”

If the teacher expressed concern or reluctance to administer the shock, they were prodded by the experimenter with increasing force, saying: “The shocks may be painful but they’re not dangerous. It is absolutely essential that we continue, Teacher. You have no other choice. Continue, please. The experiment requires that you go on. Continue.”

All the teachers put through the experiment expressed doubt, resistance, and even refusal. But no matter their protests, they were instructed to continue. Up until the 300-volt mark, every teacher continued to administer the shocks. Every single one. Sixty-five percent of the teachers continued to administer the shocks to the highest voltage, despite evidence that they were causing severe agony and pain to the learner.

This was so hard for me to believe, and yet these participants came from all walks of life. Milgram wrote, “This is, perhaps, the most fundamental lesson of our study: Ordinary people, simply doing their jobs, and without any particular hostility on their part, can become agents of a terrible destructive process.”

In the years since, there has been some controversy surrounding those original results. For example, it was uncovered that some of the results from the Milgram experiment were not reported and that the results depended on diﬀerent factors, such as whether the experiment was run at an institution like Yale as opposed to a more informal place, or that the physical distance between the teacher and the experimenter mattered. Like in all experiments, one must be careful with interpretations, and one must be mindful of the limitations of the study. But even with all of these caveats, one thing became exceedingly clear from this experiment and other later experiments that aimed to replicate the results.2 Under the right conditions, good people could do bad things.

I’d always thought of Nazis as evil, and many were, but now I had to wonder: How many Nazis were ordinary citizens, people just like me, responding to a severe situation? Of course, many were psychopaths, but some were not. Suddenly, it wasn’t just about good people and bad people. It wasn’t even about aggressive people and peaceful people. It was about people and their environment.

Environment, by definition, refers to the surroundings in which we operate: the natural world, the built world, and the interpersonal dynamics around us.

I wondered what I would do, given extreme external circumstances. This dark, disconcerting thought kept me up at night. I stared at my dorm room ceiling. I talked to my roommate, Matt, about the results and to other friends in the dorm. “These were ordinary people,” I kept saying. “Administering these shocks just because they were pressured to.” If humans weren’t just good or evil, what were we?

The Milgram experiment brought into focus some of the other big questions we were studying in psychology: How much of human nature is fixed

and inborn, and how much gets shaped and changed based on parenting, culture, and our individual experiences? Did we have any free will, after all?

There’s a long history of thought about all of this, of course, and whole books dedicated to the question of “nature versus nurture,” but I’ll give you the highlights here, because it’s relevant to this book.

These were some of the ideas I was starting to grapple with as a kid in my dorm room. It sparked an existential crisis. One that would change not only the course of my study, but of my life: I had just realized that perhaps there was no fundamental diﬀerence between myself and some of the Nazis who’d tried to kill my grandparents. People weren’t necessarily born good or evil. There was something else that made us who we are—and made us behave in good and evil ways. Was this something under our control? Was it something we could harness to prevent future evil?

NATURE AND NURTURE

There are two historical views of how we become who we are. The first idea was that we humans get all of our traits from our environment and experiences. It was termed tabula rasa—or “blank slate”—by the philosopher and physician John Locke in 1690. We will call this the nurture hypothesis. His idea was that a newborn baby starts from zero, or a blank slate, and as they grow up, their traits are imprinted on them by the outside world—their personality, their knowledge base, everything.

The second idea was that we humans get all our traits from our genetics. We will call this the nature hypothesis. That came later, when the Victorian-era philosopher Francis Galton, a cousin of Charles Darwin’s, would point to family and twin studies to argue against Locke. Galton’s position, developed in the late 1860s and early 1870s, was that a lot more than physical traits were heritable. He claimed that other psychological traits like personality, criminality, and intelligence were heritable, too. From that underlying theory, he argued for eugenics, or the idea that society should implement a “scientifically” guided social program in which people deemed

more intelligent and who displayed less criminal behavior would be encouraged to marry and have children, while those deemed less intelligent and who displayed more criminal behavior would be encouraged to stay single and have fewer kids—or even be forbidden from having children at all. Of course, this idea of eugenics is something that I and most people would find appalling. Galton had tried to back up his eugenics ideas by pointing out that the judges, military commanders, and scientists of his era all came from just a few elite families.

The University of Michigan’s own Charles Horton Cooley, an earlytwentieth-century engineer turned sociologist, saw this kind of reasoning as hugely problematic—and misguided. He pointed out that what can look like heredity is often actually the environment. Cooley argued that privilege is passed down in many ways, and not just through our genes. He came up with a great analogy: If you have a bag of corn and beans and you plant some in depleted soil, some in richer soil, some in marshes, and some in rocky sand, well, you’ll get a huge diﬀerence in the average stalk height.3 Within the marsh or within the depleted soil, variations in height would be genetically determined, but when we compare height across environments, we would quickly see that the soil matters, too. Simply put, if you’re planted in rich soil, you’re going to have an advantage over someone planted in depleted soil. Your genetics are still going to play a role, but your environment is hugely influential.

Like good and evil, nature versus nurture was clearly a false dichotomy. Leonard Darwin, yet another member of Galton’s influential family—who either scored good genes or found himself planted in rarefied soil, but likely both—wrote in a 1913 correspondence in the Eugenics Review called “Heredity and Environment”: “I, myself, have no idea. May we not be discussing questions as illogical as inquiring what portion of the area of a rectangle is due to its width and what to its length?”4

Obviously, the area of a rectangle is a factor of both its length and width. It’s their interaction, or the multiplication of length and width, that determines area. The same is true of our observable—or phenotypic—traits like our height, which are an interaction between our genes and the envi-

ronment, something known as G × E (or gene by environment interactions; the multiplication of genes and our environment).

Contemporary science is now clear that it’s not nature versus nurture— it’s a complex interplay of heritability and malleability. It’s both nature and nurture and how they interact with each other. Studies of adopted children show that socioeconomic status (SES) of birth parents and adoptive parents both contribute to a child’s IQ score.5 Work by Jay Belsky and colleagues and also other researchers such as Terrie Moﬃtt and Avshalom Caspi have shown that people with a certain genetic makeup are more sensitive to the environment—for better or worse. For example, people with certain alleles on the promoter region (5-HTTLPR) of the serotonin transporter gene are more easily aﬀected by their environment and thus more sensitive to it.6 If their environments are more positive, with nurturing caregiving, they are less likely to develop depression than people without these alleles, but if their environments are more negative, they are more likely to develop depression than people without these alleles.7 It’s human nature and human nurture. Genes and environment. Both matter, just like the area of a rectangle is dependent on its length and width. We’re not necessarily born good or evil or somewhere in between. Our surroundings influence us. But what particular surroundings could help humanity rather than harm?

ENVIRONMENT’S EFFECT ON OUR BRAINS

Around the same time that I was learning about the Milgram experiments, I was listening to lectures about some fundamental neuroscience findings that examined how our environments and our experiences change brain physiology and morphology. This is known as experience-dependent plasticity, and it explains how our experiences can change our brain physiology. In other words, the ways that we’re nurtured can change our nature. Our experiences interact with our physiology and, in the process, change our brain structure and function. This is nature × nurture defining brain physiology, just like length × width defines the area of a rectangle.

Nobel Prize–winning neurophysiologists David Hubel and Torsten Wiesel discovered that our visual cortex, located at the back of our brain, has neurons that fire for different orientations of light.8 In seminal experiments with cats (and monkeys), Hubel and Wiesel showed anesthetized cats light of different orientations—think of a bar of light that is horizontal or vertical or tilted at some angle—while simultaneously recording how different neurons in the cats’ visual cortex responded. What they found is that some neurons fire specifically when light is oriented more horizontally versus more vertically, and there will be an orientation that will maximally excite each neuron. They termed these neurons feature detectors, where different neurons fire maximally for specific features, such as light at specific orientations. Humans have these feature detectors, too. This is good, because in our world light comes in at all different orientations, and that makes up all of the objects and things in the environment that we see.

A follow-up study showed a strong nature-nurture relationship. In the early 1970s, British researchers Colin Blakemore and Grahame Cooper raised kittens in some very extreme visual environments to examine how those environments altered the kittens’ visual cortex. Blakemore and Cooper found that if they raised kittens in artificial environments that only had vertical bars of light, many of the neurons in their visual cortex became trained to fire only for vertical bars of light, and not to light in other orientations.9 If the kittens were raised in environments that had only horizontal bars of light, many of the neurons in their visual cortex would fire for light oriented horizontally, but not vertically. Because they were only exposed to one orientation, they now could only see that orientation. This is experience-dependent plasticity at its finest—or at least its most extreme. The kittens’ experiences in the experimental settings changed what their visual cortex neurons responded to. So here, nurture, the kittens’ experiences of light in their environments, was causing changes to the kittens’ nature, the neurons and what orientation of light they responded to.

This is an extreme example of experience-dependent plasticity, and examples like these are more prevalent when organisms are younger. That’s why Blakemore and Cooper used kittens and not cats—and it’s where we