by Sam Kean
Copyright
Copyright © 2012 by Sam Kean
Cover design by Will Staehle
Cover copyright © 2012 by Hachette Book Group, Inc.
All rights reserved. In accordance with the U.S. Copyright Act of 1976, the scanning, uploading, and electronic sharing of any part of this book without the permission of the publisher constitute unlawful piracy and theft of the author’s intellectual property. If you would like to use material from the book (other than for review purposes), prior written permission must be obtained by contacting the publisher at [email protected]. Thank you for your support of the author’s rights.
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First e-book edition: July 2012
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Frontispiece illustration by Mariana Ruiz and László Németh.
ISBN 978-0-316-20297-8
CONTENTS
Welcome
Frontispiece
Epigraph
Introduction
PART I
A, C, G, T, AND YOU:
HOW TO READ A GENETIC SCORE
1. Genes, Freaks, DNA: How Do Living Things Pass Down Traits to Their Children?
2. The Near Death of Darwin: Why Did Geneticists Try to Kill Natural Selection?
3. Them’s the DNA Breaks: How Does Nature Read—and Misread—DNA?
4. The Musical Score of DNA: What Kinds of Information Does DNA Store?
PART II
OUR ANIMAL PAST:
MAKING THINGS THAT CRAWL AND FROLIC AND KILL
5. DNA Vindication: Why Did Life Evolve So Slowly—Then Explode in Complexity?
6. The Survivors, the Livers: What’s Our Most Ancient and Important DNA?
7. The Machiavelli Microbe: How Much Human DNA Is Actually Human?
8. Love and Atavisms: What Genes Make Mammals Mammals?
9. Humanzees and Other Near Misses: When Did Humans Break Away from Monkeys, and Why?
PART III
GENES AND GENIUSES:
HOW HUMANS BECAME ALL TOO HUMAN
10. Scarlet A’s, C’s, G’s, and T’s: Why Did Humans Almost Go Extinct?
11. Size Matters: How Did Humans Get Such Grotesquely Large Brains?
12. The Art of the Gene: How Deep in Our DNA Is Artistic Genius?
PART IV:
THE ORACLE OF DNA:
GENETICS IN THE PAST, PRESENT, AND FUTURE
13. The Past Is Prologue—Sometimes: What Can (and Can’t) Genes Teach Us About Historical Heroes?
14. Three Billion Little Pieces: Why Don’t Humans Have More Genes Than Other Species?
15. Easy Come, Easy Go? How Come Identical Twins Aren’t Identical?
16. Life as We Do (and Don’t) Know It: What the Heck Will Happen Now?
Epilogue: Genomics Gets Personal
Acknowledgments
About the Author
Also by Sam Kean
Notes and Errata
Selected Bibliography
Copyright
Begin Reading
Table of Contents
Copyright Page
In accordance with the U.S. Copyright Act of 1976, the scanning, uploading, and electronic sharing of any part of this book without the permission of the publisher constitute unlawful piracy and theft of the author’s intellectual property. If you would like to use material from the book (other than for review purposes), prior written permission must be obtained by contacting the publisher at [email protected]. Thank you for your support of the author’s rights.
Life, therefore, may be considered a DNA chain reaction.
—MAXIM D. FRANK-KAMENETSKII, UNRAVELING DNA
Acrostic: n., an incognito message formed by stringing together the initial letters of lines or paragraphs or other units of composition in a work.
N.B.: I’ve hidden a DNA-related acrostic in The Violinist’s Thumb—a genetic “Easter egg,” if you will. If you decode this message, e-mail me through my website (http://samkean.com/contact). Or if you can’t figure it out, e-mail me anyway and I’ll reveal the answer.
Introduction
This might as well come out up front, first paragraph. This is a book about DNA—about digging up stories buried in your DNA for thousands, even millions of years, and using DNA to solve mysteries about human beings whose solutions once seemed lost forever. And yes, I’m writing this book despite the fact that my father’s name is Gene. As is my mother’s name. Gene and Jean. Gene and Jean Kean. Beyond being singsong absurd, my parents’ names led to a lot of playground jabs over the years: my every fault and foible was traced to “my genes,” and when I did something idiotic, people smirked that “my genes made me do it.” That my parents’ passing on their genes necessarily involved sex didn’t help. The taunts were doubly barbed, utterly unanswerable.
Bottom line is, I dreaded learning about DNA and genes in science classes growing up because I knew some witticism would be coming within about two seconds of the teacher turning her back. And if it wasn’t coming, some wiseacre was thinking it. Some of that Pavlovian trepidation always stayed with me, even when (or especially when) I began to grasp how potent a substance DNA is. I got over the gibes by high school, but the word gene still evoked a lot of simultaneous responses, some agreeable, some not.
On the one hand, DNA excites me. There’s no bolder topic in science than genetics, no field that promises to push science forward to the same degree. I don’t mean just the common (and commonly overblown) promises of medical cures, either. DNA has revitalized every field in biology and remade the very study of human beings. At the same time, whenever someone starts digging into our basic human biology, we resist the intrusion—we don’t want to be reduced to mere DNA. And when someone talks about tinkering with that basic biology, it can be downright frightening.
More ambiguously, DNA offers a powerful tool for rooting through our past: biology has become history by other means. Even in the past decade or so, genetics has opened up a whole Bible’s worth of stories whose plotlines we assumed had vanished—either too much time had lapsed, or too little fossil or anthropological evidence remained to piece together a coherent narrative. It turns out we were carrying those stories with us the entire time, trillions of faithfully recorded texts that the little monks in our cells transcribed every hour of every day of our DNA dark age, waiting for us to get up to speed on the language. These stories include the grand sagas of where we came from and how we evolved from primordial muck into the most dominant species the planet has known. But the stories come home in surprisingly individual ways, too.
If I could have had one mulligan in school (besides a chance to make up safer names for my parents), I’d have picked a different instrument to play in band. It wasn’t because I was the only boy clarinetist in the fourth, fifth, sixth, seventh, eighth, and ninth grades (or not only because of that). It was more because I felt so clumsy working all the valves and lever
s and blowholes on the clarinet. Nothing to do with a lack of practice, surely. I blamed the deficit on my double-jointed fingers and splayed hitchhiker thumbs. Playing the clarinet wound my fingers into such awkward braids that I constantly felt a need to crack my knuckles, and they’d throb a little. Every blue moon one thumb would even get stuck in place, frozen in extension, and I had to work the joint free with my other hand. My fingers just didn’t do what the better girl clarinetists’ could. My problems were inherited, I told myself, a legacy of my parents’ gene stock.
After quitting band, I had no reason to reflect on my theory about manual dexterity and musical ability until a decade later, when I learned the story of violinist Niccolò Paganini, a man so gifted he had to shake off rumors his whole life that he’d sold his soul to Satan for his talent. (His hometown church even refused to bury his body for decades after his death.) It turns out Paganini had made a pact with a subtler master, his DNA. Paganini almost certainly had a genetic disorder that gave him freakishly flexible fingers. His connective tissues were so rubbery that he could pull his pinky out sideways to form a right angle to the rest of his hand. (Try this.) He could also stretch his hands abnormally wide, an incomparable advantage when playing the violin. My simple hypothesis about people “being born” to play (or not play) certain instruments seemed justified. I should have quit when ahead. I kept investigating and found out that Paganini’s syndrome probably caused serious health problems, as joint pain, poor vision, weakness of breath, and fatigue dogged the violinist his whole life. I whimpered about stiff knuckles during early a.m. marching-band practice, but Paganini frequently had to cancel shows at the height of his career and couldn’t perform in public during the last years of his life. In Paganini, a passion for music had united with a body perfectly tuned to take advantage of its flaws, possibly the greatest fate a human could hope for. Those flaws then hastened his death. Paganini may not have chosen his pact with his genes, but he was in one, like all of us, and the pact both made and unmade him.
DNA wasn’t done telling its stories to me. Some scientists have retroactively diagnosed Charles Darwin, Abraham Lincoln, and Egyptian pharaohs with genetic disorders. Other scientists have plumbed DNA itself to articulate its deep linguistic properties and surprising mathematical beauty. In fact, just as I had crisscrossed from band to biology to history to math to social studies in high school, so stories about DNA began popping up in all sorts of contexts, linking all sorts of disparate subjects. DNA informed stories about people surviving nuclear bombs, and stories about the untimely ends of explorers in the Arctic. Stories about the near extinction of the human species, or pregnant mothers giving cancer to their unborn children. Stories where, as with Paganini, science illuminates art, and even stories where—as with scholars tracing genetic defects through portraiture—art illuminates science.
One fact you learn in biology class but don’t appreciate at first is the sheer length of the DNA molecule. Despite being packed into a tiny closet in our already tiny cells, DNA can unravel to extraordinary distances. There’s enough DNA in some plant cells to stretch three hundred feet; enough DNA in one human body to stretch roughly from Pluto to the sun and back; enough DNA on earth to stretch across the known universe many, many times. And the further I pursued the stories of DNA, the more I saw that its quality of stretching on and on—of unspooling farther and farther out, and even back, back through time—was intrinsic to DNA. Every human activity leaves a forensic trace in our DNA, and whether that DNA records stories about music or sports or Machiavellian microbes, those tales tell, collectively, a larger and more intricate tale of the rise of human beings on Earth: why we’re one of nature’s most absurd creatures, as well as its crowning glory.
Underlying my excitement, though, is the other side of genes: the trepidation. While researching this book, I submitted my DNA to a genetic testing service, and despite the price tag ($414), I did so in a frivolous state of mind. I knew personal genomic testing has serious shortcomings, and even when the science is solid, it’s often not that helpful. I might learn from my DNA that I have green eyes, but then again I do own a mirror. I might learn I don’t metabolize caffeine well, but I’ve had plenty of jittery nights after a late Coke. Besides, it was hard to take the DNA-submission process seriously. A plastic vial with a candy-corn orange lid arrived in the mail, and the instructions told me to massage my cheeks with my knuckles to work some cells loose inside my mouth. I then hocked into the tube repeatedly until I filled it two-thirds full of saliva. That took ten minutes, since the instructions said in all seriousness that it couldn’t be just any saliva. It had to be the good, thick, syrupy stuff; as with a draft beer, there shouldn’t be much foam. The next day I mailed the genetic spittoon off, hoping for a nice surprise about my ancestry. I didn’t engage in any sober reflection until I went to register my test online and read the instructions about redacting sensitive or scary information. If your family has a history of breast cancer or Alzheimer’s or other diseases—or if the mere thought of having them frightens you—the testing service lets you block that information. You can tick a box and keep it secret from even yourself. What caught me short was the box for Parkinson’s disease. One of the earliest memories I have, and easily the worst of those early memories, is wandering down the hallway of my grandma’s house and poking my head into the room where my grandpa, laid low by Parkinson’s, lived out his days.
When he was growing up, people always told my father how much he looked like my grandpa—and I got similar comments about looking like my old man. So when I wandered into that room off the hallway and saw a white-haired version of my father propped in a bed with a metal safety rail, I saw myself by extension. I remember lots of white—the walls, the carpet, the sheets, the open-backed smock he wore. I remember him pitched forward to the point of almost tipping over, his smock loose and a fringe of white hair hanging straight down.
I’m not sure whether he saw me, but when I hesitated on the threshold, he moaned and began trembling, which made his voice quake. My grandpa was lucky in some ways; my grandma, a nurse, took care of him at home, and his children visited regularly. But he’d regressed mentally and physically. I remember most of all the thick, syrupy string of saliva pendulous on his chin, full of DNA. I was five or so, too young to understand. I’m still ashamed that I ran.
Now, strangers—and worse, my own self—could peek at whether the string of self-replicating molecules that might have triggered Parkinson’s in my grandfather was lurking in my cells, too. There was a good chance not. My grandpa’s genes had been diluted by my grandma’s genes in Gene, whose genes had in turn been diluted in me by Jean’s. But the chance was certainly real. I could face any of the cancers or other degenerative diseases I might be susceptible to. Not Parkinson’s. I blacked the data out.
Personal stories like that are as much a part of genetics as all the exciting history—perhaps more so, since all of us have at least one of these stories buried inside us. That’s why this book, beyond relating all the historical tales, builds on those tales and links them to work being done on DNA today, and work likely to be done tomorrow. This genetics research and the changes it will bring have been compared to a shifting ocean tide, huge and inevitable. But its consequences will arrive at the shore where we’re standing not as a tsunami but as tiny waves. It’s the individual waves we’ll feel, one by one, as the tide crawls up the shore, no matter how far back we think we can stand.
Still, we can prepare ourselves for their arrival. As some scientists recognize, the story of DNA has effectively replaced the old college Western Civ class as the grand narrative of human existence. Understanding DNA can help us understand where we come from and how our bodies and minds work, and understanding the limits of DNA also helps us understand how our bodies and minds don’t work. To a similar degree, we’ll have to prepare ourselves for whatever DNA says (and doesn’t say) about intractable social problems like gender and race relations, or whether traits like aggression and i
ntelligence are fixed or flexible. We’ll also have to decide whether to trust eager thinkers who, while acknowledging that we don’t understand completely how DNA works, already talk about the opportunity, even the obligation, to improve on four billion years of biology. To this point of view, the most remarkable story about DNA is that our species survived long enough to (potentially) master it.
The history in this book is still being constructed, and I structured The Violinist’s Thumb so that each chapter provides the answer to a single question. The overarching narrative starts in the remote microbial past, moves on to our animal ancestries, lingers over primates and hominid competitors like Neanderthals, and culminates with the emergence of modern, cultured human beings with flowery language and hypertrophied brains. But as the book advances toward the final section, the questions have not been fully resolved. Things remain uncertain—especially the question of how this grand human experiment of uprooting everything there is to know about our DNA will turn out.
PART I
A, C, G, T, and You
How to Read a Genetic Score
1
Genes, Freaks, DNA
How Do Living Things Pass Down Traits to Their Children?
Chills and flames, frost and inferno, fire and ice. The two scientists who made the first great discoveries in genetics had a lot in common—not least the fact that both died obscure, mostly unmourned and happily forgotten by many. But whereas one’s legacy perished in fire, the other’s succumbed to ice.
The blaze came during the winter of 1884, at a monastery in what’s now the Czech Republic. The friars spent a January day emptying out the office of their deceased abbot, Gregor Mendel, ruthlessly purging his files, consigning everything to a bonfire in the courtyard. Though a warm and capable man, late in life Mendel had become something of an embarrassment to the monastery, the cause for government inquiries, newspaper gossip, even a showdown with a local sheriff. (Mendel won.) No relatives came by to pick up Mendel’s things, and the monks burned his papers for the same reason you’d cauterize a wound—to sterilize, and stanch embarrassment. No record survives of what they looked like, but among those documents were sheaves of papers, or perhaps a lab notebook with a plain cover, probably coated in dust from disuse. The yellowed pages would have been full of sketches of pea plants and tables of numbers (Mendel adored numbers), and they probably didn’t kick up any more smoke and ash than other papers when incinerated. But the burning of those papers—burned on the exact spot where Mendel had kept his greenhouse years before—destroyed the only original record of the discovery of the gene.