The Triumph of Seeds (13 page)

When my seeds arrived, I opened the packages immediately and dumped a few of each kind onto the kitchen table. They were all the same species, but varied just as Mendel’s had—some were green and speckled, some brownish;
some were wrinkled, and some smooth. In nineteenth-century Moravia, Mendel had no trouble purchasing thirty-four pea varieties from his local seed vendors. I only had room to plant two, but with a little research I’d tracked down one type that Mendel himself might well have grown. The Württembergische Wintererbse, or “Württemberg winter pea,” gets its name from a former kingdom in what is now southern Germany. Rail lines connected Württemberg to nearby Moravia, and the two regions were on friendly terms when Mendel was pea shopping. They even fought on the same side during the Austro-Prussian War in 1866, the same year he published his results. While the idea of a monk puttering around in the monastery garden seems inherently peaceful, Mendel lived during tumultuous times. Europe’s aging empires strained under the weight of popular unrest and shifting political alliances, while scholars struggled with an equally pressing intellectual upheaval: the theory of evolution by natural selection.

The first printing of Charles Darwin’s
Origin of Species
sold out in a single day in 1859, and a German translation appeared within a year. Mendel’s copious notes in the monastery’s copy show that he was well aware of its contents as he toiled away on his peas. But whether or not he fully grasped the significance of what those peas were telling him remains a matter of debate. Though in hindsight he seems a genius, Mendel never achieved fame during his lifetime, and very little is known about
what he actually thought. (In what must be considered one of history’s most unfortunate housekeeping
incidents, a subsequent abbot at the monastery had all of Mendel’s notebooks and papers burned.) We do know that he was far more than a dabbler. His meticulous methods and statistical approach to science were decades ahead of their time. And he applied them not only to peas, but also to thistles, hawkweeds, and honeybees, suggesting that he really was interested in general laws of inheritance. We also know that Mendel felt he’d discovered something important. Though his paper appeared in a relatively obscure Moravian journal, he ordered forty reprints and sent them to many of the leading scientists of the day. Several of those copies have since been rediscovered,
unopened and unread.

Sunset’s
Western Garden Book
recommends planting peas an inch deep and spacing them two to four inches apart. “Plant them closer,” Eliza told me. “You’re bound to lose some to slugs.” In Moravia, gardeners face a whole range of pea pests, from slugs and snails to weevils, aphids, and the occasional marauding sparrow. Mendel no doubt overplanted his rows, too, which means he must have sown a staggering number of peas to produce the “more than 10,000 plants” he recalled examining over the course of his study. My small effort would never compete with those numbers, but I took comfort in knowing that I could have told that monk a thing or two about
picking
peas. As it happens, my one experience in commercial agriculture came at the helm of a seventeen-ton pea-harvesting combine. I drove the night shift for the entire summer after my senior year in high school, filling dump truck after dump truck with peas from six p.m. until six a.m., seven days a week. It was a slow machine, and I spent most of my time reading novels by flashlight, but if I’d had Mendel’s patience and motivation I would have been up in the hopper, counting those peas and recording every subtlety of color, shape, and size.

Revisiting Mendel’s work taught me a lot more than how many peas to plant in a row. His experiments show how profoundly seeds, and our intimate relationship with them, have influenced the way we understand the natural world. They sparked an insight into the
process of evolution that was quite different from the work of Charles Darwin, though just as meaningful.

F
IGURE
5.1.  Common pea (
Pisum sativum
). The common pea made a perfect study species for Gregor Mendel because it shows a range of easily manipulated features, including two forms of seeds, smooth and wrinkled. I
LLUSTRATION
© 2014
BY
S
UZANNE
O
LIVE
.

I
t’s no coincidence that both Darwin and Alfred Russel Wallace, co-discoverer of natural selection, had their epiphanies while traveling in far-flung places—Darwin on the
Beagle
’s long voyage, and Wallace in the Malay Archipelago. Grasping such a broad law of nature required a broad view of nature. The novelty of seeing exotic creatures spread across unknown landscapes helped both men discern patterns of life that can be obscured by familiarity. When you see it in the backyard, a finch is just a finch. But to understand the nuts and bolts of evolution, how individual traits are actually passed from one generation to the next, required a focus much closer to home. Mendel’s revelation came by reexamining a natural system
that people know better than any other. Though he never took to the farming life, he used techniques perfected by countless gardeners and farmers before him, transforming the most basic insights of agriculture into scientific laws of heredity.

When archaeologists sift through the dirt of an early settlement, they look for seeds to help pinpoint the advent of farming. If they encounter ancient grains or nuts that suddenly appear larger than the wild types, they know that someone had begun choosing plants with favorable traits. For a farmer, it’s the most natural thing in the world. I once spent an afternoon with Noah, stripping dry kernels of corn from their cobs and dropping them into a metal bowl—
kuplink, kuplank, kuplunk
. We planned on grinding them all to make cornmeal mush, but if we’d been looking for seeds to save, the choice would have been obvious. Among all those tough old ears we found one with large, fat kernels that fell from the cob with ease. Big grains, easy to process—just the kind of traits to pass on.

By Mendel’s time, plant breeding had progressed to a point where every region boasted dozens of local varieties of peas, not to mention beans, lettuce, strawberries, carrots, wheat, tomatoes, and scores of other crops. People may not have known about genetics, but everyone understood that plants (and animals) could be changed
dramatically through selective breeding. A single species of weedy coastal mustard, for example, eventually gave rise to more than half a dozen familiar European vegetables. Farmers interested in tasty leaves turned it into cabbages, collard greens, and kale. Selecting plants with edible side buds and flower shoots produced Brussels sprouts, cauliflower, and broccoli, while nurturing a fattened stem produced kohlrabi. In some cases, improving a crop was as simple as saving the largest seeds, but other situations required real sophistication. Assyrians began meticulously hand-pollinating date palms more than 4,000 years ago, and as early as the Shang Dynasty (1766–1122
BC
), Chinese winemakers had perfected a strain of millet that required
protection from cross-pollination. Perhaps no culture better expresses the instinctive link between growing plants and studying
them than the Mende people of Sierra Leone, whose verb for “experiment” comes from the phrase “trying out new rice.”

Unlike the countless plant breeders who came before him, Mendel was not content to manipulate a system he didn’t understand. His genius lay in curiosity, patience, persistence, and a considerable knack for math. Over the course of eight years, he carefully bred his peas to track the fate of specific features over many generations: stem length, pod color, flower position, and, most famously, wrinkled versus smooth seeds. By meticulously noting which parents produced what kind of offspring, he discovered that traits behaved in very predictable ways. While most of his contemporaries, including Darwin, believed that breeding led to the blending of parental types, Mendel knew that traits were passed down in discrete units. His peas taught him that every individual carries two variations of every trait, one inherited
at random from each parent. In modern terms, we say that individuals carry two
alleles
for every gene. Some alleles are
dominant
and always express themselves (e.g., smooth peas), while others are
recessive
and ride along invisibly unless an individual has two of them, a situation geneticists call
double-recessive
(e.g., wrinkled peas). Nowadays, these concepts sound at least vaguely familiar to anyone who has faced the Punnett Square exercise in a basic biology course. In fact, most textbooks use Mendel’s peas as an example: crossing pure strains of wrinkled and smooth produces smooth offspring, but the generation after that will include both smooth and wrinkled peas in a ratio of three to one. It’s a classroom exercise now, but in 1865 Gregor Mendel was the only person on the planet who understood it. After the last pea was plucked from its pod, he summarized his revolutionary findings in what must be the most famous and influential paper that, to this day, practically no one has ever read.

Within a few weeks, my peas beside the Raccoon Shack had sprouted nicely and grown beyond the reach of slugs. By June, they twined six feet up the makeshift trellis I braced against the porch, and I could see their first purple blossoms through the window behind my desk. Mendel called pea flowers “peculiar” because they
kept their vital parts hidden between two narrow petals. But it was an ideal arrangement for controlling pollination, and I followed his careful instructions, stripping off the young stamens before dusting the stigma with pollen of my own choosing. Mendel accomplished all this before the invention of the Q-tip, and by doing it his way I soon learned that the inverted pouch from one flower delivers pollen perfectly to the stigma of another. I also came to know something of the peace he must have felt in his garden, because all that famous pollination took place just as mine did—on cool spring mornings, surrounded by birdsong and blossoms.

The final step in manipulating peas involves capping the flowers with little sacks to prevent contamination. I fashioned mine from paper instead of calico, but otherwise I thought my pea bed made a pretty good facsimile of that famed Moravian garden. The process also took me right back to my days studying
almendros
in Central America. Because while they may live in the tropics and grow 150 feet tall,
almendro
trees also belong to the pea family and come festooned with purple flowers. And even though I didn’t hand-pollinate any
almendros
, my dissertation was still a direct descendant of Mendel’s experiment. He opened a window into the parentage of seeds that allowed me, 150 years later, to understand entire populations from patterns in their genes—which trees were breeding, how far their pollen had traveled, and who was moving their seeds from place to place. The tools of modern genetics might be different, but I have no doubt that Mendel would have understood exactly what I was doing in the rainforest and what it all meant. Still, I wonder if he would have been as persistent in his pollen dabbing if he’d known the disappointments that lay ahead.

To say that Mendel’s pea paper landed with a thud would be incorrect, because that analogy implies that it made any sound at all. From its publication in 1866 to the turn of the century,
Experiments in Plant Hybridization
received fewer than two dozen citations in the scientific literature. Darwin’s work, by contrast, received thousands. When Mendel presented his findings to the Natural Science Society
of Brünn, not a single question was asked. (A report of “lively” audience participation in the local newspaper is thought to have been penned by a friend, or perhaps by the monk himself.) During his lifetime, the few people who knew about Mendel’s research either doubted it or didn’t understand it, and he probably never enjoyed a single satisfying conversation about its implications. Making matters worse, he tried and failed to replicate his findings on hawkweeds, small wildflowers in the aster family that, unbeknownst to Mendel, rarely
bother with pollination at all. Instead, they produce odd, clone-like seeds that display none of the bi-parental inheritance he so meticulously documented in his peas. It was an unfortunate choice that left him even more demoralized, doubtful, and discouraged. Biographers describe the young Mendel as a genial man who was beloved by his students and fond of practical jokes. But in his later years he reportedly withdrew more and more from society as well as from science. In 1878, a traveling seed dealer could not persuade the aging monk to even talk about heredity: “It is strange that when I asked Mendel about his work with the peas, he deliberately
changed the subject.”

Though it’s impossible to know what Mendel was thinking, one anecdote suggests that he maintained confidence in his results and sensed the impact they would eventually have. Long after the monk’s death in 1884, a colleague at the abbey recalled his fondness for a particular saying: “My time will surely come.”