She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity (30 page)

After a few weeks, Pickrell and his colleagues sent me a pie chart of my ancestry:

As I pored over the numbers, I grew unsettled. Thinking about all the stories I had told myself about my ancestry since I was young, I realized how often they had let me down.

Names have let me down particularly hard. If your name was Carl Zimmer, you might assume you were German. I certainly did. In school, friends would sometimes greet me with
Guten Tag, Herr Zimmer!
But when my genealogically minded relatives traced our Zimmer ancestors back to my great-great-grandfather Wolf Zimmer, it turned out he didn't live anywhere near Germany. He lived instead in Galicia, a region in what is now the Ukraine.

If we ever manage to reach further back in the Zimmer line, we will probably discover that it vanishes within a few generations. Before the late 1700s, many eastern European Jews did not use family names. The Austro-Hungarian Empire—of which Galicia was then a part—ordered that all Jews take a name so that they could be more readily taxed. Since Yiddish was banished to private life, the Jews chose names that Austrian officials would approve. It's likely that only then did my ancestors become Zimmer. My name is a convenient fiction.

Goodspeed, my mother's name, led me to see England as the other important country of my origins. Reading Shakespeare or Sherlock Holmes tales felt like learning about where I had come from. Genealogy certainly does trace the Goodspeed name back to England. But for me, the Goodspeed name marks only a single branch among many. Pickrell and his colleagues could trace those other branches across many other parts of Europe, perhaps as far away as Spain and Italy—places that my mother's research has never led her to.

After I got these results, I paid Pickrell and his colleagues a visit to pester them with questions. If my father was Jewish, how could I be only 43 percent Ashkenazi? Did that mean that my father was only 86 percent?
Pickrell warned me that their analysis was accurate enough to unsettle my family, but not to give me the final word on my genetic inheritance. “You should treat those numbers as an approximation of reality,” Pickrell said.

Those numbers were the best he could manage at the moment, with the genomes and the methods at hand. That might change if I came back to Pickrell in ten years. By then, he expected, geneticists would be able to compare millions of human genomes. Instead of relying on variants that are fairly common in at least one population, they may be using rare variants that arose in individuals just a few generations ago and are shared only by their direct descendants.

“Now it's simply a question of a match—do you have the genetic variant or not?” Pickrell explained to me. “Everyone who shares that genetic variant descends from the same common ancestor who lived two hundred years ago. That must make life so much easier.”

Pickrell also warned me that his method could only take me back a few centuries into the past. The groups of people that existed at that time did not necessarily exist a few centuries earlier.
Ashkenazi
is the name for a particular group of people who lived in a particular place at a particular time. Before AD 1000, the Ashkenazi people did not exist. Their ancestors went by other names.

To excavate deeper into my ancestry, I'd need a different genetic shovel.

To examine the Ashkenazi-linked DNA in my genome, Dina Zielinski and Nathaniel Pearson of the New York Genome Center used another piece of
software, known as RFMix. Developed by scientists at Stanford in 2013, it searches for tiny segments of matching DNA in different people's genomes. Those segments, chopped into little pieces by many generations of meiosis, can reveal ancient kinships. RFMix can match different segments to people from different parts of the world.

“It's a quilt,” Pearson told me, “made up of a segment from one ancestor attached to a segment from another ancestor. And we're trying to figure out where those segments came from.”

Pearson and Zielinski tested my DNA against two possibilities that historians have raised for where Ashkenazi Jews came from. According to one hypothesis, they descend mainly from a kingdom in present-day southern Russia, on the northwestern banks of the Caspian Sea. These people, called the Khazars, converted to Judaism perhaps a thousand years ago. They then migrated north and west into Europe.

Many historians have dismissed the Khazar hypothesis, arguing instead that Jews were already living in Italy and France at the time when the Ashkenazi ancestors supposedly converted to Judaism far to the east. These scholars argue instead that the ancestors of Ashkenazi Jews originated in Israel and other parts of the Levant. These people traveled in waves to Italy in the age of the Roman Empire, and from there, they expanded into other parts of southern Europe. Later, when Jews became increasingly persecuted across Europe, some of them
came together in Poland to seek refuge.

Zielinski and Pearson tested these possibilities by comparing my genome to the genomes of people who would have deep kinship with me. They used genomes from people in France and Italy to look for ancestors in southern and western Europe. They also included a Russian genome to represent eastern Europe. The Khazar kingdom is long gone, and so Zielinski and Pearson used genomes from an ethnic group from the region, called the Adygei. To look for an ancestry in the Near East, they added Palestinians and Druze to the analysis.

The scientists inspected million-base-long segments of my DNA and compared them to the same segments in other people's DNA. They used RFMix to find the closest match to each piece in the genomes of the other people in their study. When they were done, they generated a color-coded map of my chromosomes for me.

Most of my chromosomes matched the genomes of southwestern Europe or the Near East. A few segments showed a Russian ancestry, and even fewer resembled the Adygei. My genome offers no support for the Khazar theory of the Jews.

Zielinski and Pearson carried out only a small-scale study on my DNA—an act of scientific generosity, really. Pearson warned me not to look
at their results as the last word on my ancestry. “We have to have tons of grains of salt on the table,” he said.

Salt notwithstanding, Pearson and Zielinski's results jibed nicely with a much bigger study carried out in 2016 by
Shai Carmi of Hebrew University in Jerusalem and his colleagues. They looked at 252,358 single-nucleotide polymorphisms in the DNA of 2,540 Ashkenazi Jews, 543 Europeans, and 293 people from the Near East. Carmi and his colleagues couldn't study each genome as deeply as Zielinski and Pearson had. But they could compare many more people, hailing from many more regions.

Using RFMix and other software, they concluded that Ashkenazi Jews can trace roughly half their ancestry to the Near East, while the other half comes from Europe. The researchers found hints of two separate pulses of mixing. The first occurred in southern Europe—Italy looks like a strong possibility. The second occurred more recently, bringing together Ashkenazim with northern or eastern Europeans.

While there are a lot of uncertainties in Carmi's study, it also aligns with historical evidence that the Ashkenazi people emerged through a long migration, with plenty of mingling along the way. My parents are part of an ancient tradition.

While some of my father's ancestors may have come from the Near East into Europe a thousand years ago, my mother's ancestors were probably there long beforehand. Genetic genealogy can't take me back very far into that history, nor can it lead me to the Stone Age villages where my European ancestors lived. But I can be confident that my European roots run deep. In other words—to resort to the language of censuses—I'm white.

White
makes sense as the name of a cultural group, but as a biological label, it's just
as dubious as terms like
black
and
Hispanic
. We tend to think of whites as the pale-skinned people of Europe and their descendants, a group of humans joined together on one continent, sharing the same uniform heredity that reaches back for tens of thousands of years. The people
who lived in Europe twenty thousand years ago might be different in the ways they lived, hunting woolly rhinos instead of posting pictures on Instagram. But we still think of them as white. As scientists have examined the DNA of Europeans—both people who live on the continent today and those who lived there tens of thousands of years ago—they've demonstrated just how wrongheaded those notions are.

In the early 1980s, a graduate student at Uppsala University in Sweden named Svante Pääbo wondered if he could extract DNA from ancient remains. In 1985, he managed to isolate a few thousand bases from a
2,400-year-old mummy of an Egyptian child. He went on to extract DNA out of far older fossils, pioneering a new field called paleogenetics. Pääbo later became the director of the Max Planck Institute for Evolutionary Anthropology, where he gathered a flock of scientists and graduate students to help him fish for more ancient genes. Other scientists built paleogenetics labs in places like Oxford, Harvard, and Copenhagen.

For years, their research was hit-or-miss. Sometimes fossils turned out to have no DNA at all, because they had fossilized in an unforgiving environment. Other fossils had too much DNA—not from humans, but from bacteria and fungi that invaded the bones after death. And even when the geneticists did find human DNA, it often turned out to belong to a technician or some other living person, from whom a flake of skin or a droplet of sweat had wafted into the lab equipment.

Pääbo and other researchers spent years improving paleogenetics. They figured out how to distinguish new, contaminating DNA from ancient material. They learned not just how to grab one particular piece of DNA from a fossil but how to grab it all, sequence it, and
assemble it into an entire genome. They even got better at picking which bones to drill for DNA. At first, geneticists had simply cut out chunks from whichever bone a museum curator considered expendable. But in the early 2010s, Ron Pinhasi, an archaeologist at University College Dublin, discovered that
one kind of bone was far better than the rest. For some reason, the hard bony case surrounding the inner ear was often rich with DNA, even when none could be found elsewhere in a skeleton.

In 2015, paleogeneticists—especially David Reich's team at Harvard University—began publishing dozens, sometimes even hundreds, of ancient European genomes at a time. The results create
a kind of genetic transect. Scientists could trace changes in DNA in Europe over more than forty thousand years, mapping them from Spain to Russia. And because this transect was made from whole genomes, each skeleton could tell scientists about thousands of its own ancestors.

The oldest fossils of modern humans in Europe, dating back forty-five thousand years, look much like the bones of living Europeans. But their DNA doesn't give any indication that any living Europeans inherited their genes. Genetically speaking, they look as if they came from a different continent altogether. It's hard to say what became of them. Their particular combination of genetic variants apparently vanished about thirty-seven thousand years ago.

At a thirty-five-thousand-year-old site in Belgium, paleoanthropologists managed to get DNA out of another skeleton. The skeleton belongs to a culture known as the Aurignacian, which existed across all of Europe that wasn't buried below the glaciers of the last Ice Age. They made tools of stone and bone, painted caves with pictures of woolly rhinoceroses, and carved lion-headed figurines. The DNA from the Belgian skeleton had a distinct genetic signature of its own, different from the oldest Europeans.

About twenty-seven thousand years ago, the Aurignacian culture disappeared from the archaeological record, replaced by a new one called the Gravettian. The Gravettian people used spears to hunt mammoths, and nets to trap small game. Reich's team got DNA from Gravettian skeletons and discovered that they, too, were a distinct people with no direct genetic link to the Aurignacians who came before. For thousands of years, the Gravettian genetic lineage was the only one to be found throughout Europe.

And then, remarkably, Aurignacian DNA made a comeback. A Spanish skeleton dating back nineteen thousand years contains a mixture of Gravettian and Aurignacian DNA. Nobody can say yet where the Aurignacian people disappeared to during the vast intervening time, or how they ended
up in Spain, or how people from two such profoundly different cultures ended up having children together. All we know is that for the next few thousand years, everyone in Europe now had genomes blended from these two sources of DNA.

About fourteen thousand years ago, this long stasis was broken. The skeletons from this age now include a third ingredient in their genome. This extra DNA shares some hallmarks with that of people who live today in the Near East. Archaeologists have found that people in the Near East were living as hunter-gatherers at the time. It's possible that as the Ice Age glaciers retreated north, people from the Near East expanded into Europe and began to interbreed with the Gravettian-Aurignacian people. And then, once more, Europe settled into a new genetic equilibrium. For another five thousand years, Europeans inherited their DNA from the same combination of ancestors.

The next wave arrived about nine thousand years ago, and these people came with some important baggage. They were not hunter-gatherers but farmers, bringing crops like wheat and barley with them, along with sheep and goats. These immigrants descended from
the first farmers, who had domesticated plants and animals some two thousand years earlier in the Near East. They were not just separated by their culture from the European hunter-gatherers; a wide gulf of ancestry separated them, too. Their common ancestors might have split apart fifty thousand years earlier.