From New York Times bestselling author Sam Kean comes more incredible stories of science, history, language, and music, as told by our own DNA.

In The Disappearing Spoon, bestselling author Sam Kean unlocked the mysteries of the periodic table. In THE VIOLINIST'S THUMB, he explores the wonders of the magical building block of life: DNA.

There are genes to explain crazy cat ladies, why other people have no fingerprints, and why some people survive nuclear bombs. Genes illuminate everything from JFK's bronze skin (it wasn't a tan) to Einstein's genius. They prove that Neanderthals and humans bred thousands of years more recently than any of us would feel comfortable thinking. They can even allow some people, because of the exceptional flexibility of their thumbs and fingers, to become truly singular violinists.

Kean's vibrant storytelling once again makes science entertaining, explaining human history and whimsy while showing how DNA will influence our species' future.

Table of Contents

  • 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?
  • 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 Avatars: What Genes Make Mammals Mammals?
    • 9: Humanzees and Near Misses: When Did Humans Break from Apes, and Why?
  • 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?
    • The Oracle of DNA: Genetics in the Past, Present, and Future
    • 13: The Past Is Prologue—Sometimes: What Can Genes Teach Us about History?
    • 14: Three Billion Little Pieces: Why Don’t Humans Have More Genes?
    • 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?


Genes, Freaks, DNA

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 of their peers. 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.

The chills came during that same winter of 1884—as they had for many winters before, and would for too few winters after. Johannes Friedrich Miescher, a middling professor of physiology in Switzerland, was studying salmon, and among his other projects he was indulging a long-standing obsession with a substance—a cottony gray paste—he’d extracted from salmon sperm years before. To keep the delicate sperm from perishing in the open air, Miescher had to throw the windows open to the cold and refrigerate his lab the old-fashioned way, exposing himself day in and day out to the Swiss winter. Getting any work done required superhuman focus, and that was the one asset even people who thought little of Miescher would admit he had. (Earlier in his career, friends had to drag him from his lab bench one afternoon to attend his wedding; the ceremony had slipped his mind.) Despite being so driven, Miescher had pathetically little to show for it—his lifetime scientific output was meager. Still, he kept the windows open and kept shivering year after year, though he knew it was slowly killing him. And he still never got to the bottom of that milky gray substance, DNA.

DNA and genes, genes and DNA. Nowadays the words have become synonymous. The mind rushes to link them, like Gilbert and Sullivan or Watson and Crick. So it seems fitting that Miescher and Mendel discovered DNA and genes almost simultaneously in the 1860s, two monastic men just four hundred miles apart in the German-speaking span of middle Europe. It seems more than fitting; it seems fated.

But to understand what DNA and genes really are, we have to decouple the two words. They’re not identical and never have been. DNA is a thing—a chemical that sticks to your fingers. Genes have a physical nature, too; in fact, they’re made of long stretches of DNA. But in some ways genes are better viewed as conceptual, not material. A gene is really information—more like a story, with DNA as the language the story is written in. DNA and genes combine to form larger structures called chromosomes, DNA-rich volumes that house most of the genes in living things. Chromosomes in turn reside in the cell nucleus, a library with instructions that run our entire bodies.

All these structures play important roles in genetics and heredity, but despite the near-simultaneous discovery of each in the 1800s, no one connected DNA and genes for almost a century, and both discoverers died uncelebrated. How biologists finally yoked genes and DNA together is the first epic story in the science of inheritance, and even today, efforts to refine the relationship between genes and DNA drive genetics forward.

Mendel and Miescher began their work at time when folk theories—some uproarious or bizarre, some quite ingenious, in their way—dominated most people’s thinking about heredity, and for centuries these folks theories had colored their views about why we inherit different traits.

Everyone knew on some level of course that children resemble parents. Red hair, baldness, lunacy, receding chins, even extra thumbs, could all be traced up and down a genealogical tree. And fairy tales—those codifiers of the collective unconscious—often turned on some wretch being a “true” prince(ss) with a royal bloodline, a biological core that neither rags nor an amphibian frame could sully.

That’s mostly common sense. But the mechanism of heredity—how exactly traits got passed from generation to generation—baffled even the most intelligent thinkers, and the vagaries of this process led to many of the wilder theories that circulated before and even during the 1800s. One ubiquitous folk theory, “maternal impressions,” held that if a pregnant woman saw something ghoulish or suffered intense emotions, the experience would scar her child. One woman who never satisfied an intense prenatal craving for strawberries gave birth to a baby covered with red, strawberry-shaped splotches. The same could happen with bacon. Another woman bashed her head on a sack of coal, and her child had half, but only half, a head of black hair. More direly, doctors in the 1600s reported that a woman in Naples, after being startled by sea monsters, bore a son with a hide of scales, who ate fish exclusively and gave off fishy odors. Bishops told cautionary tales of a woman who seduced her actor husband backstage in full costume. He was playing Mephistopheles; they had a child with hooves and horns. A beggar with one arm spooked a woman into having a one-armed child. Pregnant women who pulled off crowded streets to pee in churchyards invariably produced bed wetters. Carrying fireplace logs about in your apron, next to the bulging tummy, would produce a grotesquely well-hung lad. About the only recorded happy case of maternal impressions involved a patriotic woman in Paris in the 1790s whose son had a birthmark on his chest shaped like a Phrygian cap—those elfish hats with a flop of material on top. Phrygian caps were symbols of freedom to the new French republic, and the delighted government awarded her a lifetime pension.

Much of this folklore intersected with religious belief, and people naturally interpreted serious birth defects—cyclopean eyes, external hearts, full coats of body hair—as back-of-the-Bible warnings about sin, wrath, and divine justice. One example from the 1680s involved a cruel bailiff in Scotland named Bell, who arrested two female religious dissenters, lashed them to poles near the shore, and let the tide swallow them. Bell added insult by taunting the women, then drowned the younger, more stubborn one with his own hands. Later, when asked about the murders, Bell always laughed, joking that the women must be having a high time now, scuttling around among the crabs. The joke was on Bell: after he married, his children were born with a severe defect that twisted their forearms into two awful pincers. These crab claws proved highly heritable to their children and grandchildren, too. It didn’t take a biblical scholar to see that the iniquity of the father had been visited upon the children, unto the third and fourth generations. (And beyond: cases popped up in Scotland as late as 1900.)

If maternal impressions stressed environmental influences, other theories of inheritance had strong congenital flavors. One, preformationism, grew out of the medieval alchemists’ quest to create a homunculus, a miniature, even microscopic, human being. Homunculi were the biological philosopher’s stone, and creating one showed that an alchemist possessed the power of gods. (The process of creation was somewhat less dignified. One recipe called for fermenting sperm, horse dung, and urine in a pumpkin for six weeks.) By the late 1600s, some protoscientists had stolen the idea of the homunculus and were arguing that one must live inside each female egg cell. This neatly did away with the question of how living embryos arose from seemingly dead blobs of matter. Under preformationist theory, such spontaneous generation wasn’t necessary: homuncular babies were indeed preformed and merely needed a trigger, like sperm, to grow. This idea had only one problem: as critics pointed out, it introduced an infinite regress, since a woman necessarily had to have all her future children, as well as their children, and their children, stuffed inside her like Russian matryoshka nesting dolls. Indeed, adherents of “ovism” could only deduce that God had crammed the entire human race into Eve’s ovaries on day one. (Or rather, day six of Genesis.) “Spermists” had it even worse—Adam must have had humanity entire sardined into his even tinier sperms. Yet after the first microscopes appeared, a few spermists tricked themselves into seeing tiny humans bobbing around in puddles of semen. Both ovism and spermism gained credence in part because they explained original sin: we all resided inside Adam or Eve during their banishment from Eden and therefore all share the taint. But spermism also introduced theological quandaries—for what happened to the endless number of unbaptized souls that perished every time a man ejaculated?

However poetic or deliciously bawdy these theories were, biologists in Miescher’s day scoffed at them as old wives’ tales. These men wanted to banish wild anecdotes and vague “life forces” from science and ground all heredity and development in chemistry instead.

Miescher hadn’t originally planned to join this movement to demystify life. As a young man he had trained to practice the family trade, medicine, in his native Switzerland. But a boyhood typhoid infection had left him hard of hearing and unable to use a stethoscope or hear an invalid’s bedside bellyaching. Miescher’s father, a prominent gynecologist, suggested a career in research instead. So in 1868 the young Miescher moved into a lab run by the biochemist Felix Hoppe-Seyler, in Tübingen, Germany. Though headquartered in an impressive medieval castle, Hoppe-Seyler’s lab occupied the royal laundry room in the basement; he found Miescher space next door, in the old kitchen.

Hoppe-Seyler wanted to catalog the chemicals present in human blood cells. He had already investigated red blood cells, so he assigned white ones to Miescher—a fortuitous decision for his new assistant, since white blood cells (unlike red ones) contain a tiny internal capsule called a nucleus. At the time, most scientists ignored the nucleus—it had no known function—and quite reasonably concentrated on the cytoplasm instead, the slurry that makes up most of a cell’s volume. But the chance to analyze something unknown appealed to Miescher.

To study the nucleus, Miescher needed a steady supply of white blood cells, so he approached a local hospital. According to legend, the hospital catered to veterans who’d endured gruesome battlefield amputations and other mishaps. But either way the clinic did house many chronic patients, and each day a hospital orderly collected pus-soaked bandages and delivered the yellowed rags to Miescher. The pus often degraded into slime in the open air, and Miescher had to smell each suppurated-on cloth and throw out the putrid ones (most of them). But the remaining “fresh” pus was swimming with white blood cells.

Eager to impress—and, in truth, doubtful of his own talents—Miescher threw himself into studying the nucleus, as if sheer labor would make up for any shortcomings. A colleague later described him as “driven by a demon,” and Miescher exposed himself daily to all manner of chemicals in his work. But without this focus, he probably wouldn’t have discovered what he did, since the key substance inside the nucleus proved elusive. Miescher first washed his pus in warm alcohol, then acid extract from a pig’s stomach, to dissolve away the cell membranes. This allowed him to isolate a gray paste. Assuming it was protein, he ran tests to identify it. But the paste resisted protein digestion and, unlike any known protein, wouldn’t dissolve in salt water, boiling vinegar, or dilute hydrochloric acid. So he tried elementary analysis, charring it until it decomposed. He got the expected elements, carbon, hydrogen, oxygen, and nitrogen, but also discovered 3 percent phosphorus, an element proteins lack. Convinced he’d found something unique, he named the substance “nuclein”—what later scientists called deoxyribonucleic acid, or DNA.

Miescher polished off the work in a year, and in autumn 1869 stopped by the royal laundry to show Hoppe-Seyler. Far from rejoicing, the older scientist screwed up his brow and expressed his doubts that the nucleus contained any sort of special, non-proteinaceous substance. Miescher had made a mistake, surely. Miescher protested, but Hoppe-Seyler insisted on repeating the young man’s experiments—step by step, bandage by bandage—before allowing him to publish. Hoppe-Seyler’s condescension couldn’t have helped Miescher’s confidence (he never worked so quickly again). And even after two years of labor vindicated Miescher, Hoppe-Seyler insisted on writing a patronizing editorial to accompany Miescher’s paper, in which he backhandedly praised Miescher for “enhanc[ing] our understanding…of pus.” Nevertheless Miescher did get credit, in 1871, for discovering DNA.

Some parallel discoveries quickly illuminated more about Miescher’s molecule. Most important, a German protégé of Hoppe-Seyler determined that nuclein contained multiple types of smaller constituent molecules. These included phosphates and sugars (the eponymous “deoxyribose” sugars), as well as four ringed chemicals now called nucleic “bases”—adenine, cytosine, guanine, and thymine. Still, no one knew how these parts fit together, and this jumble made DNA seem strangely heterogeneous and incomprehensible.

(Scientists now know how all these parts contribute to DNA. The molecule forms a double helix, which looks like a ladder twisted into a corkscrew. The supports of the ladder are strands made of alternating phosphates and sugars. The ladder’s rungs—the most important part—are each made of two nucleic bases, and these bases pair up in specific ways: adenine, A, always bonds with thymine, T; cytosine, C, always bonds with guanine, G. [To remember this, notice that the curvaceous letters C and G pair-bond, as do angular A and T.])

Meanwhile DNA’s reputation was bolstered by other discoveries. Scientists in the later 1800s determined that whenever cells divide in two, they carefully divvy up their chromosomes. This hinted that chromosomes were important for something, because otherwise cells wouldn’t bother. Another group of scientists determined that chromosomes are passed whole and intact from parent to child. Yet another German chemist then discovered that chromosomes were mostly made up of none other than DNA. From this constellation of findings—it took a little imagination to sketch in the lines and see a bigger picture—a small number of scientists realized that DNA might play a direct role in heredity. Nuclein was intriguing people.

Miescher lucked out, frankly, when nuclein became a respectable object of inquiry; his career had stalled otherwise. After his stint in Tübingen, he moved home to Basel, but his new institute refused him his own lab—he got one corner in a common room and had to carry out chemical analyses in an old hallway. (The castle kitchen was looking pretty good suddenly.) His new job also required teaching. Miescher had an aloof, even frosty demeanor—someone never at ease around people—and though he labored over lectures, he proved a pedagogical disaster: students remember him as “insecure, restless…myopic…difficult to understand, [and] fidgety.” We like to think of scientific heroes as electric personalities, but Miescher lacked even rudimentary charisma.

Given his atrocious teaching, which further eroded his self-esteem, Miescher rededicated himself to research. Upholding what one observer called his “fetish of examining objectionable fluids,” Miescher transferred his DNA allegiance from pus to semen. The sperm in semen were basically nuclein-tipped missiles and provided loads of DNA without much extraneous cytoplasm. Miescher also had a convenient source of sperm in the hordes of salmon that clogged the river Rhine near his university every autumn and winter. During spawning season, salmon testes grow like tumors, swelling twenty times larger than normal and often topping a pound each. To collect salmon, Miescher could practically dangle a fishing line from his office window, and by squeezing their “ripe” testes through cheesecloth, he isolated millions of bewildered little swimmers. The downside was that salmon sperm deteriorates at anything close to comfortable temperatures. So Miescher had to arrive at his bench in the chilly early hours before dawn, prop the windows open, and drop the temperature to around 35°F before working. And because of a stingy budget, when his laboratory glassware broke, he sometimes had to pilfer his ever-loving wife’s fine china to finish experiments.

From this work, as well as his colleagues’ work with other cells, Miescher concluded that all cell nuclei contain DNA. In fact he proposed redefining cell nuclei—which come in a variety of sizes and shapes—strictly as containers for DNA. Though he wasn’t greedy about his reputation, this might have been a last stab at glory for Miescher. DNA might still have turned out to be relatively unimportant, and in that case, he would have at least figured out what the mysterious nucleus did. But it wasn’t to be. Though we now know Miescher was largely right in defining the nucleus, other scientists balked at his admittedly premature suggestion; there just wasn’t enough proof. And even if they bought that, they wouldn’t grant Miescher’s next, more self-serving claim: that DNA influenced heredity. It didn’t help that Miescher had no idea how DNA did so. Like many scientists then, he doubted that sperm injected anything into eggs, partly because he assumed (echoes of the homunculus here) that eggs already contained the full complement of parts needed for life. Rather, he imagined that sperm nuclein acted as a sort of chemical defibrillator and jump-started eggs. Unfortunately Miescher had little time to explore or defend such ideas. He still had to lecture, and the Swiss government piled “thankless and tedious” tasks onto him, like preparing reports on nutrition in prisons and elementary schools. The years of working through Swiss winters with the windows open also did a number on his health, and he contracted tuberculosis. He ended up giving up DNA work altogether.

Meanwhile other scientists’ doubts about DNA began to solidify, in their minds, into hard opposition. Most damning, scientists discovered that there was more to chromosomes than phosphate-sugar backbones and A-C-G-T bases. Chromosomes also contained protein nuggets, which seemed more likely candidates to explain chemical heredity. That’s because proteins were composed of twenty different subunits (called amino acids). Each of these subunits could serve as one “letter” for writing chemical instructions, and there seemed to be enough variety among these letters to explain the dazzling diversity of life itself. The A, C, G, and T of DNA seemed dull and simplistic in comparison, a four-letter pidgin alphabet with limited expressive power. As a result, most scientists decided that DNA stored phosphorus for cells, nothing more.

Sadly, even Miescher came to doubt that DNA contained enough alphabetical variety. He too began tinkering with protein inheritance, and developed a theory where proteins encoded information by sticking out molecular arms and branches at different angles—a kind of chemical semaphore. It still wasn’t clear how sperm passed this information to eggs, though, and Miescher’s confusion deepened. He turned back to DNA late in life and argued that it might assist with heredity still. But progress proved slow, partly because he had to spend more and more time in tuberculosis sanitariums in the Alps. Before he got to the bottom of anything, he contracted pneumonia in 1895, and succumbed soon after.

Later work continued to undermine Miescher by reinforcing the belief that even if chromosomes control inheritance, the proteins in chromosomes, not the DNA, contained the actual information. After Miescher’s death, his uncle, a fellow scientist, gathered Miescher’s correspondence and papers into a “collected works,” like some belle-lettrist. The uncle prefaced the book by claiming that “Miescher and his work will not diminish; on the contrary, it will grow and his discoveries and thoughts will be seeds for a fruitful future.” Kind words, but it must have seemed a fond hope: Miescher’s obituaries barely mentioned his work on nuclein; and DNA, like Miescher himself, seemed decidedly minor.

At least Miescher died known, where he was known, for science. Gregor Mendel made a name for himself during his lifetime only through scandal…

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Extra Violinist’s Thumb Notes

Darwin’s role in musicals, an infamous scientist’s suicide note, and other topics too discursive even for this book.

Extra Violinist’s Thumb Pictures

Toulouse-Lautrec nude on a public beach and other natural marvels.

Chromosome Puzzle

How well do you know the human chromosomes? Well enough to beat 1:00?

Gene Information

The table in all manner of sizes and shapes (including human)

A Short Video

Inspired by chapter one of the book!


"As he did in his debut bestseller, The Disappearing Spoon, Sam Kean educates readers about a facet of science with wonderfully witty prose and enthralling anecdotes....Kean's thoughtful, humorous book is a joy to read."
Publishers Weekly

"A science journalist with a flair for words...[Kean's] language is fluid and accessible, even for the science-challenged."
—Barbara Hoffert, Library Journal

"Kean is one of America's smartest and most charming science writers, and his new book could be perfect for summer readers who prefer some substance with their fun."
—Michael Schaub, National Public Radio

"The DNA molecule, Kean asserts, is the 'grand narrative of human existence'-and he boldly sets out to tell the tale, not only explaining genetics and its scientific history but linking Mendel's pea shoots to the evolution of early humans....He's crafted a lively read packed with unforgettable details."
—Sarah Zhang, Discover

"Sam Kean is the best science teacher you never had... a slew of intriguing tales, which Kean spins in light, witty prose while also placing them in a broader scientific context."
—Keith Staskiewicz, Entertainment Weekly

"Sam Kean has started to make a habit of taking scientific subjects that inhabit the outskirts of the popular imagination and reintroducing them with healthy doses of history and humanity....Anyone reading this fine book could be excused for jolting upright...with wide-eyed amazement."
—Jesse Singal, Boston Globe

"[Kean] writes with a humor and humanity that make him poised to become the next Brian Greene, maybe, or Oliver Sacks-explaining small corners of the universe one case study at a time."
—Monica Hesse, Washington Post

"The Violinist's Thumb delivers the same humor and insight--and delightful anecdotes--about DNA that Kean used to make the periodic table of the elements entertaining in his New York Times bestselling debut The Disappearing Spoon."
—Brooklyn Daily Eagle