Authors: Carl Zimmer
Charlotte's fussing faded into sleepy comfort. She looked up at me and I down at her. I realized how consumed I had become with wondering what versions of DNA she might have inherited from me. I kept my arms folded tightly around her, wondering now what sort of world she was
, clad in black, hobbled into the great hall. An audience of powerful men had assembled in the Palace of Brussels on October 25, 1555, to listen to a speech by the Holy Roman emperor Charles V. At the time, he ruled over much of Europe as well as wide swaths of the New World. A few years before, Titian had painted his portrait, astride a war horse, encased in armor, brandishing a lance. But now, at fifty-five, he had become toothless and blank-stared. As he made his way to the front of the hall, he had to lean on both a cane and Prince William of Orange. Trailing Charles was his twenty-eight-year-old son, Philip. There was no question that they were related. Father and son alike had lower jaws that jutted far forward, leaving their mouths to hang open. Their shared look was so distinctive that anatomists later named it after their dynasty: the Habsburg jaw.
Father and son climbed together up a few steps onto a dais, where they turned and
sat before the assembly. They listened to the president of the Council of Flanders announce that Charles had summoned the audience to witness his abdication. They would now have to transfer their allegiance from Charles V to Philip II, his rightful heir.
Charles then rose from the throne and put on a pair of spectacles. He read from a page of notes, reflecting on his forty-year reign. Over those decades, he had expanded his power across much of the world. In addition
to Spain, he ruled the Holy Roman Empire, the Low Countries, and much of Italy. His power extended from Mexico to Peru, where his armies had recently crushed the Inca Empire. Waves of ships rolled back east across the Atlantic, arriving at Spanish ports to unload gold and silver.
Starting in the 1540s, however, Charles had begun to flag. He developed gout and hemorrhoids. His battles now ended in fewer victories and more stalemates. Charles grew depressed, sometimes so despondent he would lock himself away in a chamber. His chief consolation was his son. Charles had put Philip in charge of Spain when he was still just a teenager, and Philip had amply proven himself fit to inherit Charles's power.
Now, in 1555, Charles was content to make him a king. As he finished his speech, he turned to Philip. “
May the Almighty bless you with a son,” he said, “to whom, when old and stricken with disease, you may be able to resign your kingdom with the same good-will with which I now resign mine to you.”
It took a couple of years for all the formalities to get squared away, for Charles to retire to a monastery that he filled with clocks, and for his son to be crowned. But during all that time, the transition rolled along smoothly. No one objected to transferring their allegiance. What could be more natural, after all, than a prince succeeding his father? For anyone else to take control of the empire would have been to defy the laws of heredity.
in Italianâoriginally came from the Latin word
The Romans did not use their word as we typically use ours today, to describe the process by which we inherit genes and other parts of our biology. They used
as a legal term, referring to the state of being an heir. “If we become heirs to a certain person,” the jurist Gaius wrote, “
that person's assets pass to us.”
It sounded simple enough, but Romans fought bitterly over heredity. Their conflicts accounted for two-thirds of all the lawsuits in Roman courts. If a wealthy man died without a will, his children would be first in line to inherit his fortuneâexcept any daughters who had married into other families. Next in line would be the father's brothers and their children, then more distantly related kin.
Rome's system was one among many. Among the Iroquois, a child might
have many mothers. In many South American societies, a child could have many fathers; any man who had sex with a pregnant woman was considered a parent to her unborn child. In some societies, kinship had meaning only through the father's line, others only through the mother's.
The ApinayÃ© of Brazil had it both ways: The men trace their ancestry back through their father's line, while the ApinayÃ© women trace theirs back through their mother's. The words people used for their kin reflected how they organized relatives into a constellation of heredity; Hawaiians, for example, could use the same term for both sisters and female cousins.
Medieval Europe inherited some of Rome's hereditary customs, but over the centuries new rules emerged. In some countries,
the sons split their father's land. In others, only the eldest inherited it. In others still, it went to the youngest son. In the early Middle Ages, daughters sometimes became heirs, too, but as the centuries passed, they were mostly shut out.
As Europe grew wealthier, new hereditary rules took hold to keep the fortunes intact. The most powerful families of all took on titles and crowns, which were handed down through hereditary succession, to a son, preferably; if not, then a daughter or perhaps a grandnephew. Sometimes the branches of a dead monarch's family would fight for the crown, justifying their claim on heredity. But these claims became hard to judge when the memories of ancestors faded.
Noble families fought this forgetting by putting their genealogies in writing. In the Middle Ages,
Venice's Great Council created the Golden Book, which every son from the prominent old families of the republic signed on his eighteenth birthday. Only those whose names were recorded in the book could become members of the council. As unbroken lines of descent from noble ancestors became more important, leading families paid artists for visual propaganda. At first they represented heredity as vertical lines, but later they started painting simple trees. They might paint the founder of a noble lineage at the base of the tree, and his descendants perched on branches. The French gave these pictures a name in honor of their forking shape:
pÃ© de grue
, meaning “crane's foot.” In English, the word became
By the 1400s, pedigrees had become instantly recognizable, as evidenced by
a pageant that was put on in 1432 to honor Henry VI of England. The king, only ten years old at the time, had been crowned king of France. On his return to London, the city came out in force to celebrate his expanded power. Giant tableaux lined his path. He passed towers and tabernacles; Londoners dressed up as Grace, Fortune, and Wisdom, as well as a multitude of angels. The centerpiece of the citywide display was a castle constructed from green jasper, displaying
a pair of trees.
One tree traced Henry's ancestry back to the early kings of both England and France. The other was a tree that traced Jesus's ancestry all the way back to King David and beyond. These trees were a blend of fact and fiction, of display and concealment. They represented only those supposed ancestors whose kinship bolstered Henry's claim to power. The trees lacked siblings and cousins, bastards and wives. The most important omission of all was the House of York, Henry's rivals to the throne. But erasing them from Henry's tree did not erase them from history. Henry VI would be murdered at forty-nine, after which the House of York seized control of England.
When Charles V abdicated in 1555, he created a pageant of his own. Father and son stood on stage, side by side. The noblemen who sat before the emperor and his prince silently endorsed the hereditary transfer of power. Perhaps, as they listened to Charles deliver his speech, they turned their gaze from father to son and back. If they settled their gaze on the royal jaws, they would not have said that Charles had
his jaw from his father. They could recognize a family resemblance, but they did not explain it with the language of thrones and estates.
To account for why Charles and Philip looked alike, sixteenth-century Europeans relied largely on
the teachings of ancient Greeks and Romans. The Greek physician Hippocrates argued that men and women both produced semen, and that new life formed when the two were mixed. That blending accounted for how children ended up with a mix of their parents' characteristics. Aristotle disagreed, believing that only men produced the seeds of life. Their seeds grew on menstrual blood inside women's bodies, developing into embryos. Aristotle and his followers believed a woman
could influence the traits of her children, but only in the way the soil can influence how an acorn grows into an oak tree. “The mother is not the true parent of the child which is called hers,” the Greek playwright
Aeschylus wrote. “She is a nurse who tends the growth of young seed planted by the true parent, the male.”
The classical world had less to say about why different parents passed down different traitsâwhy some people were tall and others short, why some were dark and others pale. One widespread notion was that new differences arose through experiencesâin other words, people could pass down a trait they acquired during their lives. In ancient Rome, for example, there was a prominent family called the Ahenobarbi. Their name means “red beard,” a trait that set them apart in bright contrast to Rome's dark-haired majority. The Ahenobarbi themselves had started out dark-haired as well, according to legend. But one day, a member of the Ahenobarbi clan, a man named Lucius Domitius, was traveling home to Rome when he encountered the demigods Castor and Pollux (otherwise known as the Gemini twins). They told Domitius to deliver news to Rome that they had won a great battle. And then Castor and Pollux stroked his cheek. With that divine touch, the beard of Domitius turned the color of bronze, and he then passed down his red beard to all his male descendants.
Hippocrates provided his medical authority to another story of acquired traits, about
a tribe known as the Longheads. A long head was a sign of nobility for the tribe, prompting parents to squeeze the skulls of newborns and wrap them in bandages. “Custom originally so acted that through force such a nature came into being,” Hippocrates said. Eventually, Longhead babies came into the world with their heads already stretched out.
Other Greeks told similar storiesâof men who lost fingers, for example, and then fathered fingerless children. “For the seed,” Hippocrates wrote, “comes from all parts of the body, healthy seed from healthy parts, diseased seed from diseased parts.” If those parts changed during a person's life, his or her seeds changed accordingly.
The place where people lived could also shape them, the Greeks believed, and even give them some of their national character. “
The people of
cold countries generally, and particularly those of Europe, are full of spirit, but deficient in skill and intelligence,” Aristotle declared. They were therefore unfit to govern themselves or others. Asians had skill and intelligence, but lacked spirit, which was why they lived under the rule of despots. “The Greeks, intermediate in geographical position, unite the qualities of both sets of peoples,” Aristotle wrote.
The theories of Aristotle and other ancient writers were preserved by Arab scholars, from whom Europeans learned of them in the Middle Ages.
In the 1200s, the philosopher Albertus Magnus declared that the temperature and humidity of people's birthplace determined the color of their skin. Indians were especially good at math, Albertus thought, because the influence of the stars was especially strong in India.
But over the next three centuries, Europeans developed a new explanation for the link between one generation and the next: They were joined by blood. Even today, Westerners still use the word
to talk about kinship, as if the two were equivalent in some obvious way. But other cultures thought of kinship in terms of other substances. On
the Malaysian island of Langkawi, to pick just one counterexample, people traditionally believed that children gained kinship through what they ate. They consumed the same milk as their siblings, and they later ate the same rice grown from the same soil. These beliefs are so strong among the Langkawi that if children from two families nurse from the same woman, a marriage between them would be considered incest.
The European concept of blood gave ancestry a different form. It sealed off kinship from the outside world. A child was born with the blood of its parents coursing through its veins, and inherited all that went with it. Philip II was fit to inherit his father's crown because he had royal blood, which came from his father, and his grandfather before that. Genealogies became bloodlines, serving as proof that noble families were not tainted with lower-class blood. The Habsburgs were especially protective of their royal blood, only marrying other members of their extended family. Charles V married Isabella of Portugal, for example; they were both grandchildren of King Ferdinand and Queen Isabella of Spain.
Before long, Europeans even began to sort animals according to their blood. Of all birds,
falcons had the noblest blood, and falconry was thus suitable to be the sport of kings. If a falcon mated with a less noble bird, the chicks were called bastards. Noblemen also became connoisseurs of dogs and horses, paying fortunes for pure-blooded breeds. For animals no less than people, inheriting noble blood meant inheriting noble traits like bravery and strength.
No experience could hide the virtue carried in the blood of man or beast. In a medieval romance called
the Roman emperor of the same name unknowingly fathers a child named Florentine, who ends up being raised by a butcher. Even in that lowly household, Florentine's noble blood cannot be masked. His adoptive father sends him to the market to sell two oxen, and Florentine trades them instead for a sparrow hawk.
In the 1400s, people began to use a new word to define a group of
animals that shared the same blood: a
. A Spanish manual from around 1430 offered breeders
tips for providing a “good race” of horse. Their stallion must “be good and beautiful and of good coat and the mare that she be large and well formed and of good coat.” Before long, people were assigned to races as well. A priest named Alfonso MartÃnez de Toledo declared in 1438 that it's easy to tell the difference between men belonging to good and bad races. It doesn't matter how they're raised, MartÃnez de Toledo said. Imagine that the son of a laborer and the son of a knight are reared together on some isolated mountain away from their parents. The laborer's son would end up enjoying working in a farm field, MartÃnez de Toledo promised, while the knight's son would take pleasure only in riding horses and sword fighting.