She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity (35 page)

“I mentioned it to an Officer,” Reverend Wasse reported, “and thereby
kept some Persons from being turn'd out of the Service.”

The military's cherishing of height helped endow it with a moral value. Tallness turned into a sign of virtue and nobility. The fact that highborn boys ended up taller than lowborns seemed no coincidence.
In England, the gap was staggering: At the end of the eighteenth century, the wealthy sixteen-year-old boys who went to the military school at Sandhurst were nearly nine inches taller than the poor boys of the same age entering the Marine Society.

At the same time, the natural philosophers of the Enlightenment began to track the growth of children, with a precision that previous generations
hadn't bothered with. The first data came from a French nobleman named Philippe Guéneau de Montbeillard. In 1759, he laid his newborn son on a table and measured him from head to toe. Every six months, except for a few gaps, he would make a new measurement of his son, switching from horizontal to vertical once the boy could stand. Montbeillard saw more than just a series of numbers in these records. They revealed an upward velocity, one that accelerated during growth spurts and later dwindled to zero.

When Montbeillard's work was published, it inspired others to make similar recordings of the height of children in schools and hospitals. As they looked at the multiplying curves, they started to see broad patterns. Children tended to grow at similar velocities even if they were of different heights. A few children broke the rule: late bloomers experienced last-minute surges, while the growth of sick children slowed down drastically, leaving them short for life.

In the early 1800s, a French physician named Louis-René Villermé realized that the height of a group of people could tell him something about their well-being. Serving as a surgical assistant in the Napoleonic Wars, Villermé observed how food shortages afflicted both soldiers and civilians. Children suffered most of all, their growth permanently stunted. When Villermé left the army and began working as a physician, he could see how peacetime ravaged the poor. Traveling across France to study textile workers, child laborers, and prisoners, Villermé became convinced that social reforms were “absolutely demanded by
conscience and humanity.” Thanks in part to his efforts, France passed a law in 1841 forbidding children between eight and twelve from working over eight hours a day, or doing any night work. School became mandatory till age twelve.

Villermé succeeded because he made his case with data. He determined the rate at which poor people died, which was gruesomely higher than the rate among the wealthy. He also tracked people's heights, measuring the stunting power of poverty. Conscripts from poor regions were shorter than ones from rich regions. In Paris, Villermé documented that the people in wealthy neighborhoods where families owned their homes were taller than in poor neighborhoods where people could only rent.

“Human height,” Villermé concluded, “becomes greater and growth takes place more rapidly, other things being equal, in proportion as the country is richer, comfort more general, houses, clothes, and nourishment better, and labour, fatigue and privation during infancy and youth less.”

It was controversial to say such things in the early 1800s. Many of Villermé's fellow doctors still followed Hippocrates, believing height was set by air and water, not economics. To advance his cause, Villermé gathered allies. One of his most important converts was a wandering astronomer named Adolphe Quetelet.

In 1823, the twenty-seven-year-old Quetelet came to Paris from Belgium to inspect the city's telescopes. He was in charge of building Belgium's first observatory, and he wanted to see how the French did it. While in Paris, Quetelet met with the greatest mathematicians of the age, people who were developing equations to track the heavens, who were finding hidden order in randomness. Quetelet enjoyed meeting Villermé and learning of his ideas about society, but Quetelet's ambitions were pointed in an entirely different direction. As soon as his observatory was finished, Quetelet would make Newton-grade discoveries about the universe. He once scribbled his motto in the margin of a book:
Mundum numeri regunt,
“
Numbers rule the world.”

But just as Quetelet was finishing his grand telescopic tour and preparing to go home, Belgium fell into a revolution. Rebels moved into his unfinished observatory, and Quetelet realized that his path to fame wasn't going to run through astronomy after all.

He decided to follow Villermé's example instead.
Quetelet turned his attention to people, hoping to find an order in the chaos that had upended his life and his country. He began building a science he called social physics. Like Villermé, he chose to study the statistics of height. Gathering large numbers of measurements of children, he searched for equations that could predict their growth velocity. As Quetelet examined his results, he was startled to see a familiar pattern. Most children were close to average height, and tall and short children were rarer. Plotted on a graph, their heights formed a curving hill, its peak centered on the average.

Quetelet had already seen this hill—known as a bell curve—in the heavens. To calculate the speed of a planet, astronomers would watch it travel across a glass etched with two parallel lines, timing how long it took to move from one line to the other. If two astronomers observed the same planet, they often ended up with different figures for its speed. One astronomer might be slow to check his pocket watch, the other too quick. If the measurements of many astronomers were plotted on a single graph, they formed a bell curve as well.

On his trip to Paris, Quetelet had met mathematicians who had derived an astonishing proof about astronomical bell curves. Even if most astronomers were wrong in their measurements, the average of all their observations ended up being close to the true value. Quetelet came to see a special power in the peaks of bell curves. And when he saw his height measurements form a bell curve as well, he decided that the average height was humanity's ideal. Anyone shorter or taller than average was flawed. He extended this same importance to every other trait in the human body, from weight to the shape of the face. If there was one person who combined all the qualities of “the average man,” Quetelet said in 1835, that individual would “
represent all which is grand, beautiful, and excellent.”

Word of Quetelet's research spread across Europe. The theory he applied to height—known as the law of error—could also bring order to many other kinds of statistics, be they crime records or weather patterns. Francis Galton saw the law of error as a revolutionary advance for all of science. “
It reigns with serenity and in complete self-effacement amidst the wildest confusion,” he said. “The huger the mob, and the greater the apparent anarchy, the more perfect is its sway. It is the supreme law of Unreason.”

Galton set about measuring British heights. He invented a purpose-built device for the task, complete with a sliding vertical board, pulleys, and counterweights. He had it manufactured and then sent to teachers across England, along with instructions for how to use it on their students. When
they sent back their measurements to Galton, he ended up with a bell curve much like Quetelet's.

To Galton, these two curves looked like evidence that height was inherited. Only heredity, he believed, could account for the fact that he drew a bell curve of height a generation after Quetelet drew his. Galton couldn't say how heredity was re-creating the same curve in each generation, though. He also recognized a massive paradox he didn't yet know how to solve. “
The large do not always beget the large, nor the small the small,” he noted, “and yet the observed proportions between the large and the small in each degree of size and in every quality, hardly varies from one generation to another.”

To tackle this paradox, Galton pioneered
a new way of studying heredity. While Mendel was tracing isolated, all-or-nothing traits from one generation to the next, Galton set out to study a trait that graded smoothly from one extreme to the other. His work on this paradox would be the most important of his career. Long after his calls for eugenics became a source of shame, his work on height remains part of the foundation of today's research on heredity.

For his new project, Galton needed more than just a bell curve of height. He needed a way to compare the height of one generation to its descendants. “
I had to collect all my data for myself,” he later recalled, “as nothing existed, so far as I know, that would satisfy even my primary requirement.”

When Galton described his project to Darwin and others, they urged him to start simple. Rather than study human height, he should raise peas and measure their diameter. If he had to study animals, it would be better to study the wingspan of moths. Galton gave the sweet peas a go, taking over Darwin's garden to grow enough plants for his research. The initial measurements he got were promising. But Galton grew impatient waiting for the plants to develop, and decided it would actually be faster for him to collect data on human height—“to say nothing of its being more interesting by far than one of sweet peas or moths,” he added.

Galton posted a newspaper advertisement, asking for family records and promising prize money for the best entries. He sent cards to his friends,
requesting they ask brothers for their heights. In the 1880s, he gathered more data by turning his research into something of a carnival attraction, setting up a public laboratory at the 1884 International Health Exhibition in London. He had handbills printed up and passed around, describing the lab as being “for the use of
those who desire to be accurately measured in many ways, either to obtain timely warning of remediable faults in development, or to learn their powers.” Over the course of a year, Galton's staff measured 9,337 people at the exhibition. In 1888, he set up a similar lab at the Science Galleries of the South Kensington Museum and examined thousands more. Galton had their height measured, along with many other traits, from their hearing to their hand strength.

A “computer”—a woman who could carry out fast, accurate calculations by hand—worked her way through Galton's thousands of height records, organizing them on a grid. Each column represented the combined average height of the parents (including an adjustment for the shorter height of the mothers). The rows represented the height of the children. The computer put a number in each square to show the number of families with each combination of heights.

Galton would often stare at this grid, trying to make sense of it. In some regions, the grid was blank. Some squares had only one family marked inside them. Others had dozens. Finally, staring at the grid one day as he waited for a train, it came to him. The numbers formed a football-shaped cloud. They clustered around an invisible straight line that extended from the lower left corner to the upper right. The taller parents were, the taller their children tended to be. Some parents had children who were shorter or taller than they were. Very short parents had children who grew taller than they were, and vice versa, drawing their children closer to the average.

Like Mendel, Galton had discovered a profound pattern of heredity. But he was no more clear about what it meant. Galton tried to explain his results by arguing that each child inherited less than half of each trait from each parent. They somehow inherited the remainder from even older ancestors. That extra inheritance, Galton claimed, pulled children back away
from the extremes toward the ancestral average. While Galton's “ancestral inheritance” would eventually be proven wrong, his discovery of heredity's signature remains a tremendous accomplishment.

In the 1890s, a young colleague of Galton's named
Karl Pearson recognized the importance of his work and gave it a proper mathematical makeover. Pearson invented a formula that let him put a number on how closely children resembled their parents. He could use the same formula to compare siblings as well. To try out his equation on real children, Pearson enlisted his own squadron of teachers to measure the height of their students (along with other traits like the circumference of their heads and the span of their arms). He found that the traits were correlated. In other words, pairs of brothers would tend to have similar traits, presumably due to heredity.

Right around the time that Pearson was developing these new mathematical techniques, Mendel came back to light. A coalition of geneticists, the Mendelians, dismissed the measurements that Galton and Pearson were making. It was more important to them to study heredity the way Mendel did, by tracking recessive and dominant traits. Pearson gathered allies of his own. His coalition—known as the biometricians—accused the Mendelians of being time wasters who were obsessing over the few oddball traits that happen to fall in line with Mendel's simple law. A trait like height was not either/or. People were not either tall or short as Mendel's peas might be smooth or wrinkled. Pearson called for a more powerful explanation for heredity to account for this sort of smooth variation.

In 1918, a British statistician named Ronald Fisher brokered a peace between the Mendelians and the biometricians. He demonstrated that the two kinds of heredity were
opposite sides of the same coin. The variation in a trait could be influenced by one gene, or a few, or many. The difference between a wrinkled pea and a smooth one that Mendel studied would turn out to be controlled by variants of a single gene. But a trait like height, with a smooth distribution from short to tall, was likely the result of variations in many genes. People could inherit a vast number of different possible combinations of variants, and for most people, the combined effects of all
those variants would leave them close to average. Fewer people ended up very tall or short. The result would be Quetelet's bell curve.

Fisher also found an elegantly mathematical way to take into account the fact that genes do not have sole control over traits such as height. Along with nature, nurture might have a part to play. Fisher argued that the overall variation in a trait could be the result of both genetic variation as well as variations in the environment. Genetic variation might be strong for some traits, and environmental variation might be more important for others. The fraction caused by genetic variation—in other words, the variation that could be inherited through genes—came to be known as heritability. If genetic variation has no influence over the variation in a trait, then its heritability is zero. If the environment has no influence, then the heritability is 100 percent.