Lisa Feldman Barrett - Seven and a Half Lessons About the Brain

Copyright 2020 by Lisa Feldman Barrett

Illustrations by Flow Creative (flowcs.com)

All rights reserved

For information about permission to reproduce selections from this book, write to or to Permissions, Houghton Mifflin Harcourt Publishing Company, 3 Park Avenue, 19th Floor, New York, New York 10016.

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Library of Congress Cataloging-in-Publication Data

Names: Barrett, Lisa Feldman, author.

Title: Seven and a half lessons about the brain / Lisa Feldman Barrett.

Description: Boston : Houghton Mifflin Harcourt, 2020. | Includes bibliographical references and index. | Summary: From the author of How Emotions Are Made, a myth-busting primer on the brain, in the tradition of Seven Brief Lessons on Physics and Astrophysics for People in a HurryProvided by publisher.

Identifiers: LCCN 2020023431 (print) | LCCN 2020023432 (ebook) | ISBN 9780358157144 (hardcover) | ISBN 9780358157120 (ebook)

Subjects: LCSH: BrainPopular works. | NeurosciencesPopular works.

Classification: LCC QP376 .B357 2020 (print) | LCC QP376 (ebook) | DDC 612.8/2dc23

LC record available at https://lccn.loc.gov/2020023431

LC ebook record available at https://lccn.loc.gov/2020023432

Cover design by Martha Kennedy

Cover photograph Christoph Burgstedt / Science Source

Author photograph Mark Karlsberg / Studio Eleven

Droodles excerpted from The Ultimate Droodles Compendium: The Absurdly Complete Collection of All the Classic Zany Creations of Roger Price. Copyright 2019 by Tallfellow Press, Inc. Used by permission. All rights reserved.

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To Barb Finlay
and my other colleagues
who taught me the craft of neuroscience,
for their great generosity and even
greater patience

I wrote this book of short, informal essays to intrigue and entertain you. Its not a full tutorial on brains. Each essay presents a few compelling scientific nuggets about your brain and considers what they might reveal about human nature. The essays are best read in order, but you can also read them out of sequence.

As a professor, I usually include loads of scientific details in my writing, such as descriptions of studies and pointers to journal papers. For these informal essays, however, Ive moved the full scientific references to my website, sevenandahalflessons.com.

Also, at the end of this book, youll find an appendix with selected scientific details. It offers a bit more depth on some essay topics, explains that certain points are still debated by scientists, and gives credit to other people for some interesting turns of phrase.

Why are there seven and a half lessons rather than eight? The opening essay tells a story of how brains evolved, but it is just a brief peek into a vast evolutionary historyhence, half a lesson. The concepts that it introduces are critical to the rest of the book.

I hope youll enjoy learning what one neuroscientist thinks is fascinating about your brain and how that three-pound blob between your ears makes you human. The essays dont tell you what to think about human nature, but they do invite you to think about the kind of human you are or want to be.

O NCE UPON A TIME , the Earth was ruled by creatures without brains. This is not a political statement, just a biological one.

One of these creatures was the amphioxus. If you ever glimpsed one, youd probably mistake it for a little worm until you noticed the gill-like slits on either side of its body. Amphioxi populated the oceans about 550 million years ago, and they lived simple lives. An amphioxus could propel itself through the water, thanks to a very basic system for movement. It also had an exceedingly simple way of eating: it planted itself in the seafloor, like a blade of grass, and consumed any minuscule creatures that happened to drift into its mouth. Taste and smell were of no concern because an amphioxus didnt have senses like yours. It had no eyes, just a few cells to detect changes in light, and it could not hear. Its meager nervous system included a teeny clump of cells that was not quite a brain. An amphioxus, you could say, was a stomach on a stick.

Amphioxi are your distant cousins, and theyre still around today. When you look at a modern amphioxus, you behold a creature very similar to your own ancient, tiny ancestor who roamed the same seas.

Can you picture a little wormy creature, two inches long, swaying in the current of a prehistoric ocean, and glimpse humanitys evolutionary journey? Its difficult. You have so much that the ancient amphioxus did not: a few hundred bones, an abundance of internal organs, some limbs, a nose, a charming smile, and, most important, a brain. The amphioxus didnt need a brain. Its cells for sensing were connected to its cells for moving, so it reacted to its watery world without much processing. You, however, have an intricate, powerful brain that gives rise to mental events as diverse as thoughts, emotions, memories, and dreamsan internal life that shapes so much of what is distinctive and meaningful about your existence.

Why did a brain like yours evolve? The obvious answer is to think. Its common to assume that brains evolved in some kind of upward progressionsay, from lower animals to higher animals, with the most sophisticated, thinking brain of all, the human brain, at the top. After all, thinking is the human superpower, right?

Well, the obvious answer turns out to be wrong. In fact, the idea that our brains evolved for thinking has been the source of many profound misconceptions about human nature. Once you give up that cherished belief, you will have taken the first step toward understanding how your brain actually works and what its most important job isand, ultimately, what kind of creature you really are.

Amphioxi were not our direct ancestors, but we had a common ancestor that was very likely similar to a modern-day amphioxus.

Five hundred million years ago, as little amphioxi and other simple creatures continued to dine serenely on the ocean floor, the Earth entered what scientists call the Cambrian period. During this time, something new and significant appeared on the evolutionary scene: hunting. Somewhere, somehow, one creature became able to sense the presence of another creature and deliberately ate it. Animals had gobbled one another before, but now the eating was more purposeful. Hunting didnt require a brain, but it was a big step toward developing one.

The emergence of predators during the Cambrian period transformed the planet into a more competitive and dangerous place. Both predators and prey evolved to sense more of the world around them. They began to develop more sophisticated sensory systems. Amphioxi could distinguish light from dark, but newer creatures could actually see. Amphioxi had simple skin sensation, but newer creatures evolved a fuller sense of their body movements in the water and a greater sense of touch that allowed them to detect objects by vibration. Sharks today still use this kind of touch sense to locate prey.

With the arrival of greater senses, the most critical question in existence became Is that blob in the distance good to eat, or will it eat me? Creatures who could better sense their surroundings were more likely to survive and thrive. The amphioxus may have been a master of its environment, but it couldnt sense that it had an environment. These new animals could.

The hunters and the hunted also received a boost from another new ability: more sophisticated kinds of movement. For the amphioxus, whose nerves for sensing and moving were woven together, movement was extremely basic. Whenever its stream of food became a trickle, it wriggled in a random direction to plant itself in another spot. Any looming shadow prompted its body to dart away. In the new world of hunting, however, predators and prey alike began to evolve more capable systems for movement, or motor systems, to navigate with greater speed and dexterity. These newer animals could dart, turn, and dive deliberately toward things like food and away from things like threats in ways that suited their environment.