The Gene: An Intimate History - Siddhartha Mukherjee Page 0,24

inherited one copy from each parent—one allele from father, via sperm, and one from mother, via the egg. When a hybrid was created, both traits existed intact—although only one asserted its existence.

Between 1857 and 1864, Mendel shelled bushel upon bushel of peas, compulsively tabulating the results for each hybrid cross (“yellow seeds, green cotyledons, white flowers”). The results remained strikingly consistent. The small patch of land in the monastery garden produced an overwhelming volume of data to analyze—twenty-eight thousand plants, forty thousand flowers, and nearly four hundred thousand seeds. “It requires indeed some courage to undertake a labor of such far-reaching extent,” Mendel would write later. But courage is the wrong word here. More than courage, something else is evident in that work—a quality that one can only describe as tenderness.

It is a word not typically used to describe science, or scientists. It shares roots, of course, with tending—a farmer’s or gardener’s activity—but also with tension, the stretching of a pea tendril to incline it toward sunlight or to train it on an arbor. Mendel was, first and foremost, a gardener. His genius was not fueled by deep knowledge of the conventions of biology (thankfully, he had failed that exam—twice). Rather, it was his instinctual knowledge of the garden, coupled with an incisive power of observation—the laborious cross-pollination of seedlings, the meticulous tabulation of the colors of cotyledons—that soon led him to findings that could not be explained by the traditional understanding of inheritance.

Heredity, Mendel’s experiments implied, could only be explained by the passage of discrete pieces of information from parents to offspring. Sperm brought one copy of this information (an allele); the egg brought the other copy (a second allele); an organism thus inherited one allele from each parent. When that organism generated sperm or eggs, the alleles were split up again—one was passed to the sperm, and one to the egg, only to become combined in the next generation. One allele might “dominate” the other when both were present. When the dominant allele was present, the recessive allele seemed to disappear, but when a plant received two recessive alleles, the allele reiterated its character. Throughout, the information carried by an individual allele remained indivisible. The particles themselves remained intact.

Doppler’s example returned to Mendel: there was music behind noise, laws behind seeming lawlessness, and only a profoundly artificial experiment—creating hybrids out of purebred strains carrying simple traits—could reveal these underlying patterns. Behind the epic variance of natural organisms—tall; short; wrinkled; smooth; green; yellow; brown—there were corpuscles of hereditary information, moving from one generation to the next. Each trait was unitary—distinct, separate, and indelible. Mendel did not give this unit of heredity a name, but he had discovered the most essential features of a gene.

On February 8, 1865, seven years after Darwin and Wallace had read their papers at the Linnean Society in London, Mendel presented his paper, in two parts, at a much less august forum: he spoke to a group of farmers, botanists, and biologists at the Natural Science Society in Brno (the second part of the paper was read on March 8, a month later). Few records exist of this moment in history. The room was small, and about forty people attended. The paper, with dozens of tables and arcane symbols to denote traits and variants, was challenging even for statisticians. For biologists, it may have seemed like absolute mumbo jumbo. Botanists generally studied morphology, not numerology. The counting of variants in seeds and flowers across tens of thousands of hybrid specimens must have mystified Mendel’s contemporaries; the notion of mystical numerical “harmonies” lurking in nature had gone out of fashion with Pythagoras. Soon after Mendel was done, a professor of botany stood up to discuss Darwin’s Origin and the theory of evolution. No one in the audience perceived a link between the two subjects being discussed. Even if Mendel was aware of a potential connection between his “units of heredity” and evolution—his prior notes had certainly indicated that he had sought such a link—he made no explicit comments on the topic.

Mendel’s paper was published in the annual Proceedings of the Brno Natural Science Society. A man of few words, Mendel was even more concise in his writing: he had distilled nearly a decade’s work into forty-four spectacularly dreary pages. Copies were sent to the Royal Society and the Linnean Society in England, and to the Smithsonian in Washington, among dozens of institutions. Mendel himself requested forty reprints, which he mailed, heavily annotated, to many scientists. It