The Gene: An Intimate History - Siddhartha Mukherjee Page 0,27

unbroken, unbreakable message? De Vries had not encountered Mendel’s paper yet. But like Mendel, he began to scour the countryside around Amsterdam to collect strange plant variants—not just peas, but a vast herbarium of plants with twisted stems and forked leaves, with speckled flowers, hairy anthers, and bat-shaped seeds: a menagerie of monsters. When he bred these variants with their normal counterparts, he found, like Mendel, that the variant traits did not blend away, but were maintained in a discrete and independent form from one generation to the next. Each plant seemed to possess a collection of features—flower color, leaf shape, seed texture—and each of these features seemed to be encoded by an independent, discrete piece of information that moved from one generation to the next.

But de Vries still lacked Mendel’s crucial insight—that bolt of mathematical reasoning that had so clearly illuminated Mendel’s pea-hybrid experiments in 1865. From his own plant hybrids, de Vries could dimly tell that variant features, such as stem size, were encoded by indivisible particles of information. But how many particles were needed to encode one variant trait? One? One hundred? A thousand?

In the 1880s, still unaware of Mendel’s work, de Vries edged toward a more quantitative description of his plant experiments. In a landmark paper written in 1897, entitled Hereditary Monstrosities, de Vries analyzed his data and inferred that each trait was governed by a single particle of information. Every hybrid inherited two such particles—one from the sperm and one from the egg. And these particles were passed along, intact, to the next generation through sperm and egg. Nothing was ever blended. No information was lost. He called these particles “pangenes.” It was a name that protested its own origin: even though he had systematically demolished Darwin’s theory of pangenesis, de Vries paid his mentor a final homage.

While de Vries was still knee-deep in the study of plant hybrids in the spring of 1900, a friend sent him a copy of an old paper drudged up from the friend’s library. “I know that you are studying hybrids,” the friend wrote, “so perhaps the enclosed reprint of the year 1865 by a certain Mendel . . . is still of some interest to you.”

It is hard not to imagine de Vries, in his study in Amsterdam on a gray March morning, slitting open that reprint and running his eyes through the first paragraph. Reading the paper, he must have felt that inescapable chill of déjà vu running through his spine: the “certain Mendel” had certainly preempted de Vries by more than three decades. In Mendel’s paper, de Vries discovered a solution to his question, a perfect corroboration of his experiments—and a challenge to his originality. It seemed that he too was being forced to relive the old saga of Darwin and Wallace: the scientific discovery that he had hoped to claim as his own had actually been made by someone else. In a fit of panic, de Vries rushed his paper on plant hybrids to print in March 1900, pointedly neglecting any mention of Mendel’s prior work. Perhaps the world had forgotten “a certain Mendel” and his work on pea hybrids in Brno. “Modesty is a virtue,” he would later write, “yet one gets further without it.”

De Vries was not alone in rediscovering Mendel’s notion of independent, indivisible hereditary instructions. That same year de Vries published his monumental study of plant variants, Carl Correns, a botanist in Tübingen, published a study on pea and maize hybrids that precisely recapitulated Mendel’s results. Correns had, ironically, been Nägeli’s student in Munich. But Nägeli—who considered Mendel an amateur crank—had neglected to tell Correns about the voluminous correspondence on pea hybrids that he had once received from “a certain Mendel.”

In his experimental gardens in Munich and Tübingen, about four hundred miles from the abbey, Correns thus laboriously bred tall plants with short plants and made hybrid-hybrid crosses—with no knowledge that he was just methodically repeating Mendel’s prior work. When Correns completed his experiments and was ready to assemble his paper for publication, he returned to the library to find references to his scientific predecessors. He thus stumbled on Mendel’s earlier paper buried in the Brno journal.

And in Vienna—the very place where Mendel had failed his botany exam in 1856—another young botanist, Erich von Tschermak-Seysenegg, also rediscovered Mendel’s laws. Von Tschermak had been a graduate student at Halle and in Ghent, where, working on pea hybrids, he had also observed hereditary traits moving independently and discretely, like particles, across generations of