Read She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity Online
Authors: Carl Zimmer
Among Bakewell's international admirers was
Frederick Augustus III, the Elector of Saxony. In 1765, Frederick received an extraordinary gift from the king of Spain: 210 Merino sheep. Frederick wanted to use the Merinos to build a thriving sheep industry in Saxony, but he worried that
the livestock might not thrive outside of Spain. He consulted with Bakewell about his plan.
Bakewell assured Frederick that the traits carried in a sheep's blood would endure through generations no matter where they were bred, as long as they were properly raised. Frederick discovered Bakewell was right, and soon Germany was producing so much fine Merino wool that it could satisfy much of the demand from English factories and had enough left over to support a textile industry of its own. Around Moravia, at the heart of this new industry, a new generation of sheep breeders were inspired to achieve even more. They believed that if they could exploit the laws of heredity, they'd be able to breed even better sheep. But first they'd have to discover those laws.
In 1814 the breeders founded an organization, the title of which wasâdeep breathâ“
The Association of Friends, Experts and Supporters of Sheep Breeding for the achievement of a more rapid and more thoroughgoing advancement of this branch of the economy and the manufacturing and commercial aspects of the wool industry that is based upon it.” Those who didn't want to lose too much oxygen uttering the full name simply called it the Sheep Breeders' Society.
The Sheep Breeders' Society was based in the city of Brno in Moravia (now part of the Czech Republic). They held regular meetings drawing members from as far as Hungary and Silesia. The city also hosted the Brno Pomological Society, a group of plant breeders who hoped to bring similar improvements to crops. The plant breeders had a Bakewell of their own to emulate, an English gentleman named
Thomas Andrew Knight.
In the late 1700s, Knight applied Bakewell's sheepish doctrine to the flocks on his English estate and was pleased with the results. He then set out to apply the same principles to plants. His plan was to hand-fertilize plants with pollen grains. The pollenâthe botanical equivalent of spermâwould make their way inside of flowers to their ovulesâthe equivalent of eggs. Knight would use different varieties for his experiments in order to make hybrids. And he would then use Bakewell's in-and-in breeding methods until their heredity became stable.
At first, Knight crossed apple trees. They grew so slowly that he couldn't tell if his procedure was actually working. Around 1790, Knight searched for another species that could return him faster results.
None appeared so well calculated to answer my purpose,” he later wrote, “as the common pea.”
Knight was delighted to discover that his hybrid peas flowered, producing seeds that could develop into plants of their own, quickly growing high in his garden. He was also intrigued by the way traits of the parents reappeared in descendants. When he fertilized white peas with pollen of a gray-seeded variety, for example, the hybrid plant bore gray seeds.
“By this process, it is evident, that
any number of new varieties may be obtained,” Knight declared. If breeding was carried out scientifically, he was convinced, England need never go hungry. “
A single bushel of improved wheat or peas may in ten years be made to afford seed enough to supply the whole island,” he declared.
No one in England was able to make Knight's hope come true. But in Brno, plant breeders kept trying, collaborating with sheep breeders to uncover biology's mysteries. In 1816, the Sheep Breeders' Society organized a series of public debates about the nature of heredity. Some members argued that the environment impressed traits on offspring. A Hungarian count named Imre Festetics took the opposing view. Based on years of sheep breeding, he argued that healthy animals pass on their characteristics to their offspring. He observed a pattern much like what Knight had seen in peas: The traits of grandparents could disappear from their lambs, only to reappear in the following generation.
Festetics even argued that freaks of nature could leap back into a pedigree after many generations of healthy sheep. He warned against using those freaks for breeding. Inbreeding could improve flocks of sheep, Festetics declared, but only if breeders first carefully selected the stock they used. In an 1819 manifesto, Festetics urged that his fellow breeders determine the nature of these patterns scientifically, uncovering what he called “
genetic rules of nature.”
In later years, the Moravian breeders followed Festetics's advice. They
designed breeding experiments, guided by the latest discoveries coming out of Germany's universities. One of the busiest research centers was a local Augustinian priory, led by the abbott Cyrill Franz Napp.
Napp and his friars got into the breeding business
to pay off the priory's massive debts, and they came to enjoy great success with sheep and crops. Yet Napp complained that breeding was “
a lengthy, troublesome and random affair.”
The trouble would not go away until breeders changed their ways. “
What we should have been dealing with is not the theory and process of breeding,” Napp declared at an 1836 meeting of the Sheep Breeders' Society, “but the question should be: what is inherited, and how?”
His scientific frame of mind led Napp to set his friars loose on scientific questions. They studied how to forecast the weather, maintained a large collection of minerals, and built a massive scientific library. Napp set aside part of the grounds solely to grow rare species of plants. A monk named Matthew KlÃ¡cel ran experiments in another gardenâat least until his radical philosophy on nature forced him to flee to the United States. When young men entered the Augustinian order, Napp encouraged them to immerse themselves in the latest scientific advances. One of the young men in whom Napp took a special interest was a poor farmer's son named Gregor Mendel.
Mendel's first job at the priory was to teach languages, math, and science in a local school. He proved so good at it that Napp sent him to the University of Vienna for more training. Mendel took a course in physics there in which he learned how to design careful experiments, and another in botany, where he learned about the long-running debate over hybrid plants and whether two species could cross to produce a new species. When Mendel returned to the priory in 1853, he continued to teach, but his time at the university inspired him to take up scientific research. He ran the friary's weather station and investigated the possibility of communicating weather reports with
semaphore flags or telegraph messages. He raised honeybees, studied sunspots, and invented chess problems. And he carried on Napp's own research by breeding plants. Mendel cross-pollinated fruit trees, raised prizewinning fuchsias, and bred varieties of beans and peas.
In 1854, Napp gave Mendel permission to run a large-scale experiment that Mendel hoped would make some sense of hybridization. The randomness that bedeviled the breeding societies might be hiding some hidden order. Mendel followed Knight's example, and planted his garden with peas.
For his experiment, Mendel grew twenty-two varieties of peas, each with a set of distinctive traits reliably passed from ancestors to descendants. He raised the plants in a greenhouse, where they couldn't be randomly pollinated by visiting bees. Mendel patiently crossed the varieties, moving pollen from one line to another. His experiment was gigantic, involving more than ten thousand plants, because he had learned in his physics classes that big samples are statistically more likely to reveal important patterns.
In one of his first experiments, Mendel crossed yellow and green plants. When he opened the pods, he got a result similar to what Knight had found sixty years before. All the peas inside were yellow. Mendel then transferred pollen between these hybrids and produced a second generation. Now only some of the peas were yellow. A fraction of the plants displayed the green color that had disappeared from sight in the previous generation.
When Mendel counted the peas, he found about three yellow plants for every green one. He then selected plants from the second generation that produced yellow peas and crossed them with the original line of yellow plants. Some of their offspring produced green peas once more. Mendel got similar results when he compared wrinkly peas to smooth ones, or tall plants to short ones.
In 1865, Mendel talked about his experiment at a meeting of Brno's Natural History Society. To make sense of the three-to-one ratio he found so often in peas, he proposed that every plant contained
a pair of “antagonistic elements.” When a plant produced pollen or ovules, each one received only one of those elements. And when a pollen grain fertilized an ovule, the new plant inherited its own pair of the elements. Each element could give rise to a particular trait in a plant. One might produce a green color, while another produced yellow. But Mendel argued that some elements were stronger than others. As a result, a hybrid plant with one yellow element and a green one would be yellow, because yellow is dominant over green.
This scheme could account for the three-to-one ratio, thanks to the way the elements were passed down from parents to offspring. When Mendel mated two yellow hybrids together, each plant contributed one of its two elements to each offspring. Which element a particular offspring inherited was a matter of chance. There were thus four combinations: yellow/yellow, yellow/green, green/yellow, and green/green. Working through these figures, Mendel calculated that a quarter of the plants would inherit the yellow element from both parents. Half would inherit one yellow and one greenâand also end up looking yellow. Meanwhile, the remaining quarter would inherit two green elements.
Mendel's talks did not set his audience's hair on fire. None of them were so inspired by his experiments to repeat them. In hindsight, it's easy to recognize the importance of his results, but at the time they didn't stand out from the many other studies of hybrids that were also being carried out. A mentor of Mendel, the Swiss botanist Carl NÃ¤geli, encouraged him to see if the same patterns would emerge in another species, suggesting hawkweed.
It turned out to be a bad suggestion, thanks to hawkweed's peculiar biology. When Mendel crossed hawkweed plants, he didn't produce the three-to-one ratio again. Instead, the hawkweed often reverted back to one of the ancestral forms Mendel had started with, and he was unable to alter their descendants any further. The experiment didn't make Mendel abandon his ideas about antagonistic elements, however. He added a new speculation: In hawkweed, the elements didn't get separated as pollen and ovules developed.
“Evidently we are here
dealing only with individual phenomena,” Mendel wrote to NÃ¤geli, “which are the manifestation of a higher, more fundamental, law.”
That law would eventually bear Mendel's name. But in the years after Mendel published his experiments, only a few other researchers cited them. One day, when Mendel was standing in his hawkweed garden with a friend, he predicted he would be proven right eventually. “My time is yet to come,” he said.
When Napp died in 1868, his protÃ©gÃ© succeeded him, and before long,
the newly appointed
Abbot Mendel got so ensnared in tax battles with the government that he had to abandon his experimental garden. When he died sixteen years later, in 1884, his funeral was attended by throngs of peasants and the poor. But no scientists turned up to mourn his passing.
Breeders in the United States took a different path. The American colonies produced no Bakewell of their own. No scientific breeding society emerged in the early republic to debate how precisely sheep inherited fatty mutton. American plant breeders did not set up experimental gardens to test the boundaries of species. Instead, the United States became an arena for capitalist competition as farmers battled one another with breeds they hoped would make them a fortune.
Many of those breeds were imported from Europe to the New World. In the early 1800s, thousands of Merino sheep were illegally smuggled from Spain to Vermont. The legends about the Merino prompted New England sheep farmers to abandon their flocks for the new imports.
By 1837, there were a million Merinos in Vermont alone.
The American booms typically went bust. Merino speculators became convinced that textile mills would develop a bottomless appetite for wool, and the price for a single lamb
climbed beyond a thousand dollars. When the Merino bubble popped, Americans promptly turned for salvation to exotic chickensâBlack Polands, White Dorkings, Yellow Shanghaeâuntil the
hen fever broke, too.
Along with new animal breeds, American farmers searched for new crop varieties. They typically didn't make crosses like Knight or Mendel did. Instead, they would simply stumble across a peculiar plant. Some farmers would keep their discoveries to themselves, so as to attract more customers when they sold their goods at local markets. Others sent off their discoveries to the new seed catalog companies, hoping to get rich on orders. In Iowa, a Quaker farmer named
Jesse Hiatt noticed a little apple tree growing between the rows of his orchard. He chopped the seedling down, but the following year it had returned. He cut it down again, and it returned
once more. “If thee must grow, thee may,” Hiatt reportedly told the tree. After ten years, the tree finally bore fruit: handsome, red-and-yellow-streaked apples with a crisp, sweet flavor. He shipped some to Missouri, to enter a contest run by Stark Bro's company. His apples won the contest, and Stark Bro dubbed his variety Delicious. It became one of their most successful varieties, and it remains so today.
Luther Burbank was born into this land of breeding in 1849. His first memory of his mother, he later recalled, was of her setting him down in a meadow at their Massachusetts farm
while she gathered strawberries. Within a few years, Luther had farm work of his own to do: “
the wood to bring, weeds to pull, chickens to feed, the cows to drive to pasture,” he later wrote. Yet Luther still had time left over to build waterwheels and bark canoes. He inspected the apple trees in the family's orchard, learning how to spot the difference between the Baldwins and Greenings. He observed the swelling buds as they cast off brown coats and opened their pink-and-white petals. When Luther became a teenager, he planted his own garden, writing to his older brother, who had moved to California, to send him the seeds of exotic Western breeds.