The Gene: An Intimate History - Siddhartha Mukherjee Page 0,32

synthesized all his observations into his most mature hypothesis on heredity. He proposed that every feature in a human—height, weight, intelligence, beauty—was a composite function generated by a conserved pattern of ancestral inheritance. The parents of a child provided, on average, half the content of that feature; the grandparents, a quarter; the great-grandparents, an eighth—and so forth, all the way back to the most distant ancestor. The sum of all contributions could be described by the series—1/2 + 1/4 + 1/8 . . .—all of which conveniently added to 1. Galton called this the Ancestral Law of Heredity. It was a sort of mathematical homunculus—an idea borrowed from Pythagoras and Plato—but dressed up with fractions and denominators into a modern-sounding law.

Galton knew that the crowning achievement of the law would be its ability to accurately predict a real pattern of inheritance. In 1897, he found his ideal test case. Capitalizing on yet another English pedigree obsession—of dogs—Galton discovered an invaluable manuscript: the Basset Hound Club Rules, a compendium published by Sir Everett Millais in 1896, which documented the coat colors of basset hounds across multiple generations. To his great relief, Galton found that his law could accurately predict the coat colors of every generation. He had finally solved the code of heredity.

The solution, however satisfying, was short-lived. Between 1901 and 1905, Galton locked horns with his most formidable adversary—William Bateson, the Cambridge geneticist who was the most ardent champion of Mendel’s theory. Dogged and imperious, with a handlebar mustache that seemed to bend his smile into a perpetual scowl, Bateson was unmoved by equations. The basset-hound data, Bateson argued, was either aberrant or inaccurate. Beautiful laws were often killed by ugly facts—and despite how lovely Galton’s infinite series looked, Bateson’s own experiments pointed decidedly toward one fact: that hereditary instructions were carried by individual units of information, not by halved and quartered messages from ghostly ancestors. Mendel, despite his odd scientific lineage, and de Vries, despite his dubious personal hygiene, were right. A child was an ancestral composite, but a supremely simple one: one-half from the mother, one-half from the father. Each parent contributed a set of instructions, which were decoded to create a child.

Galton defended his theory against Bateson’s attack. Two prominent biologists—Walter Weldon and Arthur Darbishire—and the eminent mathematician Karl Pearson joined the effort to defend the “ancestral law,” and the debate soured quickly into an all-out war. Weldon, once Bateson’s teacher at Cambridge, turned into his most vigorous opponent. He labeled Bateson’s experiments “utterly inadequate” and refused to believe de Vries’s studies. Pearson, meanwhile, founded a scientific journal, Biometrika (its name drawn from Galton’s notion of biological measurement), which he turned into a mouthpiece for Galton’s theory.

In 1902, Darbishire launched a fresh volley of experiments on mice, hoping to disprove Mendel’s hypothesis once and for all. He bred mice by the thousands, hoping to prove Galton right. But as Darbishire analyzed his own first-generation hybrids, and the hybrid-hybrid crosses, the pattern was clear: the data could only be explained by Mendelian inheritance, with indivisible traits moving vertically across the generations. Darbishire resisted at first, but he could no longer deny the data; he ultimately conceded the point.

In the spring of 1905, Weldon lugged copies of Bateson’s and Darbishire’s data to his vacation in Rome, where he sat, stewing with anger, trying, like a “mere clerk,” to rework the data to fit Galtonian theory. He returned to England that summer, hoping to overturn the studies with his analysis, but was struck by pneumonia and died suddenly at home. He was only forty-six years old. Bateson wrote a moving obituary to his old friend and teacher. “To Weldon I owe the chief awakening of my life,” he recalled, “but this is the personal, private obligation of my own soul.”

Bateson’s “awakening” was not private in the least. Between 1900 and 1910, as evidence for Mendel’s “units of heredity” mounted, biologists were confronted by the impact of the new theory. The implications were deep. Aristotle had recast heredity as the flow of information—a river of code moving from egg to the embryo. Centuries later, Mendel had stumbled on the essential structure of that information, the alphabet of the code. If Aristotle had described a current of information moving across generations, then Mendel had found its currency.

But perhaps an even greater principle was at stake, Bateson realized. The flow of biological information was not restricted to heredity. It was coursing through all of biology. The transmission of hereditary traits was just one