She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity (34 page)

That DNA reveals that Denisovans were most closely related to Neanderthals, not modern humans. They split from a common ancestor as long as 470,000 years ago. In 2017, Pääbo and his colleagues examined the mutations in four Denisovan individuals and estimated that the oldest individual who lived in the Denisova cave was there over 100,000 years ago. The youngest known Denisovan lived there about 50,000 years ago.

Like Neanderthals, Denisovans have left their genetic mark on living humans. The people who carry the highest amounts of Denisovan DNA—in some cases more than 5 percent—live in Australia, New Guinea, and nearby Pacific Islands. Scientists have also found tiny amounts of Denisovan DNA in the genomes of East Asians and Native Americans. Paradoxically, the people who live today near the Denisova cave have hardly any Denisovan DNA at all in their genes.

These clues all point in the same direction: We should think of Denisovans as the eastern Neanderthals. When the common ancestors of Neanderthals and Denisovans spread out across Eurasia, they diverged into two populations. The Neanderthals headed west into Europe, while the Denisovans went the other way. It's possible they reached Southeast Asia, where they later encountered modern humans on their way to the Pacific.

For the most part,
Denisovan DNA was as ill-suited to modern humans as the DNA of Neanderthals. But a few Denisovan genes may have provided benefits of their own.
One of the best candidates for a beneficial Denisovan gene is called EPAS1. It regulates how many red blood cells our bodies make and how they transport oxygen. Tibetans carry a variant of EPAS1 that protects them from the dangers of life at high altitudes. In 2014,
Emilia Huerta-Sanchez and Rasmus Nielsen at the University of California, Berkeley, discovered that the Tibetan form of EPAS1 came from Denisovans. We can't know if Denisovans were adapted for living at high elevations; it's entirely possible that their variant of EPAS1 helped them in some other way, and just happened to prove useful when the ancestors of Tibetans moved toward the sky.

To hear Gronau say that he found some Denisovan DNA in me didn't make sense. It had been unsettling enough for geneticists to say I might be Italian. Did my Denisovan DNA mean that I had some hidden ancestry in the highlands of New Guinea?

“Yeah,” Hubisz said offhandedly, poring over her own laptop. “I found it, too.”

With a grin, Siepel turned to me. “How are you at high altitudes?” he asked.

Siepel cautioned me that the risk of errors goes up when scientists try to look tens of thousands of years into our genealogical past. Some of my DNA might look Denisovan to Siepel's computer because scientists have yet to find the same sequence in Neanderthal fossils. And even if I do carry some Denisovan DNA, that may not mean that my modern human ancestors made direct contact with Denisovans. It's entirely possible that Denisovans and Neanderthals mated. Later, some Neanderthal descendant passed on that Denisovan DNA to my own ancestors.

“Still, you can't exclude the possibility that you have some Denisovan DNA,” said Siepel.

By midday, we were done inspecting my genome and hungry for lunch. Gronau signed off from Israel, and Hubisz, Siepel, and I stood up to stretch our legs. “I wish there was more of a punch line,” Hubisz said. “We found a lot of data.”

“Well,” Siepel said, looking on the bright side, “we found that he was part alien.”

I
N
THE
LATE
1990
S
, Joel Hirschhorn became a pediatric endocrinologist at Boston Children's Hospital. As an expert on hormones, he saw a lot of children with diabetes. But he saw almost as many children who were short. “You have parents coming in with their child, and they're worried because their child is not growing quickly—or as quickly as their friends,” Hirschhorn told me when I paid him a visit in his office.

Being very short is sometimes a sign of a serious medical problem—an inability to make growth hormone, for example. Mostly, though, Hirschhorn spent his visits with short children calming their parents. “You would end up saying there's probably nothing wrong,” he said. “And I would say a good majority of the time, one or both of the parents themselves are short. And so you would just explain how height is inherited.”

Hirschhorn would tell the parents about their genes, and how they had given some of them to their children. “You have some versions that make you a little on the shorter side, and you passed some of those to your child, so now they're probably going to end up a little on the shorter side,” he said.

The parents sometimes asked Hirschhorn about those genes. He would say that he could be sure there were genes involved, but he couldn't name them. Nobody knew their identity. “And about the twentieth time,” Hirschhorn said, “I thought to myself: We could find out what those genes are.”

In addition to his work as a doctor, Hirschhorn was doing research on
the side. Working at the Whitehead Institute nearby, he developed new methods for pinpointing genetic variants that caused medical conditions such as diabetes. Compared to such disorders, height seemed like an easy thing to study. Diabetes, for instance, takes years to develop, depending in part on what people eat. It's also possible that there are different sets of genes that can make different groups of people at risk for it. Height, by contrast, is simple: It's easy to measure, and you can measure it in anyone. Hirschhorn thought he could just compare tall and short people, look at their DNA, and find the variants that tended to raise or lower their height.

In 2004, Hirschhorn left the Whitehead and moved to the next building over, joining the Broad Institute to continue to study height. And when I visited him at the Broad in 2017, he was still studying height. He had just gotten a new office, which was almost completely bare. He had a phone and a laptop. On a whiteboard, someone had written
Flour
and
Flower.
Hirschhorn looked about as close to average height as a man could be.

During the seventeen years that Hirschhorn had been studying height, he explained, he and his colleagues had made progress. Now his conversations with parents sound a little different. “Instead of saying, ‘we don't know what they are,' I usually say, ‘we know what some of them are.'”

But if parents came to Hirschhorn with the DNA sequence of their child and asked him how tall their child would become, he still wouldn't be able to tell them. “It's not implausible that we could be there at some point—at least before I retire,” he told me.

As I have worked on this book, my daughters have gotten taller. They have entered that phase of life in which they start looking down at their relatives, one by one. There's usually at least one back-to-back comparison at every family gathering. Our girls stand at military attention, the rest of us squinting across the crowns of their heads and patting down their hair. Throughout their growth spurts, Charlotte and Veronica have been good sports. You can tell that they are indulging us, that they don't pay much mind to their increasing height—certainly not compared to an upcoming recital or the insufferable wait for the revival of
The
Gilmore Girls
. I can see
something of myself when they roll their eyes and smile politely at their height-obsessed elders.

I remember the years when my brother, Ben, and I were barreling upward. The lines that our parents drew on the kitchen doorframe were like the hands of a clock, tracking family time. The jump from one line to the next made clear that both Ben and I were going to outgrow our mother, then our father. As I reached six foot, and Ben six foot one, our heights became a marvel among our shorter relatives. They would tilt their heads up to take in our stature. Sensing an unaccustomed crane, they'd ask, “Where did you
get
that from?” They would vaguely recall a towering great-grandfather, or try to remember the story a great-aunt told about a tall cousin. They searched our genealogy for
someone
from whom we might have inherited our own height. They talked about height as if it were a diamond that an ancestor could have stored away in a safe-deposit box, where it could sit for a century until Ben and I brought it out into the light again.

Sometimes heredity does act with a diamond-like simplicity. Two defective copies of the PAH gene will cause PKU. But heredity's influence is usually much harder to decipher. It's hidden in clouds of complexity, a complexity generated both within our genes and outside of our bodies. It's hard to imagine anything simpler than height. It's nothing but a number, one that can be obtained with a hardware-store tape measure at that. And yet the heredity of height can be as baffling as quantum physics. Light can be at once a particle and waves. Height can be at once shaped by heredity and governed by our experience. Height was among the first puzzles that early scientists of heredity tried to take apart, and yet they haven't finished solving it yet.

All of written history is laced with stories of giants and dwarves. The Bible describes races of giants who lived before the Flood.
Og, king of Bashan, slept in an iron bed measuring nine cubits (thirteen and a half feet). In other stories from around the Near East, Og and his height also appear. According to one tale, he escaped the Great Flood by wading
alongside the ark, the oceans lapping around his knees. In another, one of his bones was laid across a river to serve as a bridge.

The ancient Greeks and Romans would sometimes unearth dinosaur bones and house them in temples, believing them to belong to the skeletons of humanlike giants. They also marveled at the true giants who walked among them, exaggerating their stature with each retelling. According to Pliny the Elder, two men who stood ten feet tall settled in Rome during the reign of Augustus. Similar reports of extraordinarily tall people popped up from time to time all the way into the Renaissance. A seventeenth-century physician named Platerus claimed he once met a man in Luxembourg “
nine foot high complete.”

By the 1700s, tall people had become professional attractions. In 1782,
an Irishman named Charles Byrne, standing eight foot two, dazzled London society. He had been born a normal-size baby, but had quickly begun to grow far faster than other boys. The people in his village said that he grew so tall because his parents had conceived him atop a haystack. As a teenager, Byrne toured fairs around Ireland before traveling to England to make his fortune.

“
This truly amazing phenomenon is indisputably the most extraordinary production of the human species ever beheld since the days of Goliath,” ran one London newspaper ad. Clad in a frock coat, knee breeches, silk stockings, and frilled cuffs, “the Irish Giant” received paying visitors twice a day, six days a week, in a handsome apartment. Byrne earned more than seven hundred pounds before dying at age twenty-two, reportedly from excessive drinking. “The whole tribe of surgeons put in a claim for the poor departed Irish Giant,” one newspaper reported, “and surrounded his house just as Greenland harpooners would an enormous whale.”

At the other end of height's spectrum,
people with dwarfism were also singled out, sometimes for reverence but more often for great cruelty. In ancient Egypt, dwarves served Pharaohs as sacred dancers, jewelers, textile makers, and priests. The chiefs of some West African tribes appointed dwarves as their attendants, perceiving a connection between them and the gods. The Romans had a brutal fascination, watching dwarf gladiators fight
to the death or keeping male and female dwarves around their houses like pets. Often the dwarves simply wandered the houses of their masters, naked except for jewels around their necks. In the 1500s, an Italian noblewoman named Isabella d'Este built miniature marble-lined apartments in her enormous palace to house a colony of dwarves. They would entertain her by performing somersaults, or pretending to be priests, or pissing drunkenly on the floor.

In time, some dwarves were accorded more dignity in European society, although they were no less fetishized. At the royal courts of countries such as England and Russia, dwarves served as royal painters, nurses, and diplomats. Dwarves competed with giants for audiences in the eighteenth century. In 1719, a man named Robert Skinner, who reportedly stood just over two feet high, met an equally short woman, Judith, while they were traveling from exhibit to exhibit. They fell in love, got married, and retired from touring. Their fourteen children all grew to normal height. Somehow, the Skinners' stature had failed to imprint itself on their family.

Twenty-three years after they met, the Skinners ran out of money and went back to London in 1742 to earn some more. This time, they displayed not only themselves but their towering children. The mismatch so astonished London society that the Skinners made a small fortune over the course of two years and were able to retire for good. They spent their retirement traveling around St. James's Park in a custom-built carriage pulled by two dogs and driven by a twelve-year-old boy clad in purple-and-yellow livery.

The Skinners stood out, even within their own family. But there also were rumors since ancient times of
entire races of miniature people. According to some stories, they lived in India—or maybe it was Africa—and rode miniature horses into battle against cranes. The forests of northern Europe were reputed to be rife with dwarves and gnomes. Off the coast of England, one of the Hebrides islands was known as the Isle of Pigmies; underneath a chapel, it was told, several miniature human bones had once been dug up.

In 1699, a British anatomist named Edward Tyson tried to dash these
stories. Having performed the first dissection of a chimpanzee, Tyson declared that “the pygmies of the Ancients were a sort of Apes, and not of Humane Race.” It wasn't until the mid-1800s that European explorers in Africa encountered groups of humans, such as the Baka and Mbuti, who typically never grow taller than five feet. It turned out there were slivers of truth embedded in the old fantasies.

In other parts of the world, European explorers sent back reports of towering peoples. Ferdinand Magellan rounded the southern tip of South America in 1520 and, in the words of his chronicler Antonio Pigafetta, spotted “a giant who was on the shore, quite naked, and who danced, leaped, and sang, and while he sang he threw sand and dust on his head.” Magellan claimed that the giant's tribe—which came to be known as the Patagonians—stood ten feet tall. A century later, Sir Francis Drake visited the Patagonians and dismissed that measurement as a lie. The Patagonians were clearly just seven feet tall, Drake said.

With more time, the giants of the world shrank to more realistic heights. Nevertheless, the fact remained that people in some countries were taller than others. In 1826, the British ethnologist James Cowles Prichard observed that the Irish, although not especially tall on average, produced a remarkable number of giants like Charles Byrne. “We can hardly avoid the conclusion that
there must be some peculiarity in Ireland which gives rise to these phenomena,” he said.

Prichard believed the peculiarity had something to do with the land of Ireland rather than its people. He subscribed to an idea that dated back at least to Hippocrates. “
Such as dwell in places which are low-lying, abounding in meadows and ill ventilated, and who have a larger proportion of hot than of cold winds, and who make use of warm waters—these are not likely to be of large stature,” Hippocrates explained. Tall people, Hippocrates said, were “such as inhabit a high country, and one that is level, windy, and well-watered.”

Hippocrates was well aware that his patients, who all lived in Greece, grew to different heights. He ascribed their differences to the changing weather, which could disrupt the concentration of a man's semen, altering
his child's development. “This process cannot be the same in summer as in winter, nor in rainy as in dry weather,” Hippocrates declared.

Ancient Greeks seem to have thought about height only in rough figures. “
In about five years, in the case of human beings at any rate, the body seems to gain half the height that is gained in all the rest of life,” Aristotle wrote. Even in the Renaissance, scholars didn't see the need for precision. In 1559,
the Italian physician Pavisi declared that “the growth of infants and children is quite swift, and often in two or three years they add two or three cubits.” Three cubits would be four and a half feet. Either Pavisi didn't pay very close attention to infants, or he lived among giants.

The Enlightenment brought a new rigor to measuring height. In 1708, Great Britain enacted the Recruiting Act, requiring that army conscripts be at least five foot five. In 1724, one Reverend Mr. Wasse wrote to the Royal Society to warn that measuring height might be harder than the army realized. Reverend Wasse fixed a nail above a chair high enough that he could just barely touch it with his fingertips. He then pushed a garden roller for half an hour. When the reverend sat down again, a half-inch gap lay between his hand and the nail. Apparently, he had shrunk during his exercise. Reverend Wasse reported to the Royal Society that he also measured the height of “a great many sedentary People and Day-Labourers.” He found that people could grow taller and shorter over the course of a day—by as much as an inch in some cases.