The Gene: An Intimate History - Siddhartha Mukherjee Page 0,21

genes were best suited for survival.

The particular details of Jenkin’s story were ugly—perhaps deliberately so—but its conceptual point was clear. If heredity had no means of maintaining variance—of “fixing” the altered trait—then all alterations in characters would eventually vanish into colorless oblivion by virtue of blending. Freaks would always remain freaks—unless they could guarantee the passage of their traits to the next generation. Prospero could safely afford to create a single Caliban on an isolated island and let him roam at large. Blending inheritance would function as his natural genetic prison: even if he mated—precisely when he mated—his hereditary features would instantly vanish into a sea of normalcy. Blending was the same as infinite dilution, and no evolutionary information could be maintained in the face of such dilution. When a painter begins to paint, dipping the brush occasionally to dilute the pigment, the water might initially turn blue, or yellow. But as more and more paints are diluted into the water, it inevitably turns to murky gray. Add more colored paint, and the water remains just as intolerably gray. If the same principle applied to animals and inheritance, then what force could possibly conserve any distinguishing feature of any variant organism? Why, Jenkin might ask, weren’t all Darwin’s finches gradually turning gray?I

Darwin was deeply struck by Jenkin’s reasoning. “Fleeming Jenkins [sic] has given me much trouble,” he wrote, “but has been of more use to me than any other Essay or Review.” There was no denying Jenkin’s inescapable logic: to salvage Darwin’s theory of evolution, he needed a congruent theory of heredity.

But what features of heredity might solve Darwin’s problem? For Darwinian evolution to work, the mechanism of inheritance had to possess an intrinsic capacity to conserve information without becoming diluted or dispersed. Blending would not work. There had to be atoms of information—discrete, insoluble, indelible particles—moving from parent to child.

Was there any proof of such constancy in inheritance? Had Darwin looked carefully through the books in his voluminous library, he might have found a reference to an obscure paper by a little-known botanist from Brno. Unassumingly entitled “Experiments in Plant Hybridization” and published in a scarcely read journal in 1866, the paper was written in dense German and packed with the kind of mathematical tables that Darwin particularly despised. Even so, Darwin came tantalizingly close to reading it: in the early 1870s, poring through a book on plant hybrids, he made extensive handwritten notes on pages 50, 51, 53, and 54—but mysteriously skipped page 52, where the Brno paper on pea hybrids was discussed in detail.

If Darwin had actually read it—particularly as he was writing Variation and formulating pangenesis—this study might have provided the final critical insight to understand his own theory of evolution. He would have been fascinated by its implications, moved by the tenderness of its labor, and struck by its strange explanatory power. Darwin’s incisive intellect would quickly have grasped its implications for the understanding of evolution. He may also have been pleased to note that the paper had been authored by another cleric who, in another epic journey from theology to biology, had also drifted off the edge of a map—an Augustine monk named Gregor Johann Mendel.

* * *

I. Geographic isolation might have solved some of the “grey finch” problem—by restricting interbreeding between particular variants. But this would still be unable to explain why all finches in a single island did not gradually collapse to have identical characteristics.

“Flowers He Loved”

We want only to disclose the [nature of] matter and its force. Metaphysics is not our interest.

—The manifesto of the Brünn Natural Science Society, where Mendel’s paper was first read in 1865

The whole organic world is the result of innumerable different combinations and permutations of relatively few factors. . . . These factors are the units which the science of heredity has to investigate. Just as physics and chemistry go back to molecules and atoms, the biological sciences have to penetrate these units in order to explain . . . the phenomena of the living world.

—Hugo de Vries

As Darwin was beginning to write his opus on evolution in the spring of 1856, Gregor Mendel decided to return to Vienna to retake the teacher’s exam that he had failed in 1850. He felt more confident this time. Mendel had spent two years studying physics, chemistry, geology, botany, and zoology at the university in Vienna. In 1853, he had returned to the monastery and started work as a substitute teacher at the Brno Modern School. The monks who