Scatter, Adapt, and Remember: How Humans Will Survive a Mass Extinction

by Newitz, Annalee

  One might argue that Jewish identity coalesced during a period when its nation was fragmented. And the Babylonian exile was just the first of many great fragmentations recorded in Jewish history. In the first century CE, Jews fled the Romans; in the fifteenth century, they raced to outrun representatives of the Spanish Inquisition; and still later, they abandoned large parts of Europe to escape the twentieth-century Holocaust. Passover has probably remained such an important ritual because it’s designed to remind Jews of our shared history as people who scatter in order to survive. To this day, we dwell in all the far-flung places where Jewish communities large and small continue to tell stories of a legendary time when we clung to life by running as far as we could, in as many directions as we could.

  But is scattering really a good survival strategy outside of legends? If Jewish history is any guide, the answer is yes. Despite centuries of persecution and diaspora, there are people all over the world who call themselves Jews. And now we have scientific evidence that today’s Jews haven’t just inherited a cultural tradition. Some of us really do have biological ancestors who survived by wandering in the desert and beyond to find new homes. Population geneticists say there’s strong evidence that a group of Jews originating in ancient Rome over 2,500 years ago share identifiable genetic links with Jewish populations today from Spain, Syria, North Africa, Russia, and many other places. In other words, many Jews today owe their existence to people who scattered.

  The Genetic Evidence for the Diaspora

  Geneticist Harry Ostrer has contributed to one of the world’s largest and longest-running genetic studies of Jewish people. An energetic and talkative man, he collaborates with colleagues and subjects across the globe from a slightly cluttered office at the Albert Einstein College of Medicine, surrounded by family pictures and lab equipment. Located in a quiet neighborhood in the Bronx, the college is practically in the backyard of some of the groups Ostrer studies, like Brooklyn’s Syrian Jewish community, as well as a few Iraqi Jewish enclaves in Queens. He’s done work with a large group of Turkish Jews in Seattle, too.

  Studying these groups and others has given Ostrer a perspective on the results of diaspora, rather than the events leading up to it. One point he emphasized strongly was that diaspora is more often about staying rather than scattering. Jewish history can be characterized by long periods of settlement and assimilation into local cultures, punctuated by sudden shifts when many people abruptly fled to new lands, usually to escape persecution. As geneticist David Goldstein notes in his book Jacob’s Legacy: A Genetic View of Jewish History, some of the earliest historical records of the Jews come from sixth-century BCE cuneiform tablets, which describe the Babylonian conquest of Jerusalem. But the results of that diaspora are lost to history. The next great Jewish settlement took place in Rome, and the diaspora that resulted has genetic echoes all the way up into the twenty-first century. The Roman diaspora is the focus of Ostrer’s research.

  There are extensive records of Jewish culture from the Roman empire during the first century CE. Many of these Jews were brought to Rome as slaves starting in the second century BCE, from Greece, Judea (the former southern kingdom of Judah), and many areas in the region. Over the next century, Jews assimilated into Roman culture and became one of the biggest and most powerful minority groups in the empire. Though we have no reliable source for how many Jews there were in Rome, we know from contemporary sources that Judaism was a highly visible religion. Politicians issued laws regulating the practice of Judaism, and many Jews became Roman citizens. Meanwhile, in the courts, commentators often complained of Jewish “disturbances”—probably referring to political unrest in response to constantly shifting Roman rules about Jewish taxation and social status.

  Unlike today, Roman Jews expanded the ranks of their temples by actively proselytizing. They assimilated into Roman life, but Romans assimilated into Jewish traditions, too. It was a time of great cultural mixing that finally came to an end in the late first century CE, when Emperor Claudius ordered all Jews to be expelled from Rome. A few years later, some Jews in Jerusalem rebelled against the Roman control of their city and were defeated, while Roman Jews fled their homes to avoid death or worse. In the Bible, this period is referred to as the time of the Second Temple’s destruction because the Romans destroyed the house of worship on the Temple Mount just as the Babylonians had over 600 years before.

  Though this diaspora survives in historical documents and biblical stories, Ostrer wanted to know if he could track down evidence of a direct genetic connection between the Jews who left ancient Rome and the Jews alive today. To find out, he had to get DNA samples from hundreds of Jews across the world, looking for genetic commonalities. “I went to Rome and did recruitment there,” Ostrer recalled. “That’s been a stable community for hundreds of years and perhaps dates back to the community that was there in classical antiquity.” He also got samples from Eastern European Jews as well as Jews in immigrant communities in the New York area. Anybody who could trace their Jewish ancestry back two generations to all four of their grandparents was eligible to participate.

  Once he’d amassed his samples, Ostrer and his team had the beginnings of what they call the Jewish HapMap. “Hap” is short for “haplotype,” a term geneticists use to describe a set of unique genetic markers in the human genome. People who share haplotypes are more closely related to one another than people who don’t, and Ostrer wanted to know whether he could identify distinctly Jewish haplotypes. Over several years, the researchers at the Jewish HapMap Project scoured their data using a variety of statistical methods to compare both short and long strands of DNA from volunteers. They began to see patterns suggesting that people who had lived close together centuries ago still shared genetic similarities. Jews in Central Europe today share more genetically with Jews in the Middle East than a non-Jewish person living in Central Europe does with a non-Jewish person in the Middle East. And it’s all because those groups of contemporary Jews had ancestors from the same regions of Rome. Discoveries like this demonstrated that there are distinctive Jewish haplotypes that offer hints about where people’s ancestors settled in the diaspora.

  Once they had enough data, Ostrer and his colleagues could actually create genetic maps tracking the spread of Jewish haplotypes out of ancient Rome and into the Middle East and Europe. Why were they able to isolate these haplotypes at all, when so much time had passed? It had to do with a change in Jewish culture after the Roman diaspora. Jews in ancient Rome were proselytizers—they converted many people and intermarried with non-Jews regularly. The Jews of that era would probably have shared haplotypes with their Jupiter-worshipping neighbors. But after their expulsion from Rome and the destruction of Jerusalem in the first century CE, Jews changed the structure of their communities radically. No longer were they permitted to proselytize and intermarry. To be considered truly Jewish, a child had to be born of a Jewish mother, establishing a rigorous matrilineal line. Without realizing it, the Jews of the first century created a culture that allowed their unique haplotypes to endure over the next 2,000 years.

  Mapping the diaspora becomes more difficult when you add in the evidence of extensive assimilation and intermarriage taking place in Europe before the Inquisition. In countries like Spain, Jews enjoyed a social status comparable to the one they had once held in ancient Rome. They were prominent members of their cities, intermarried with non-Jews, and dramatically expanded their communities. But the tide turned in the fourteenth century, which saw the rise of political persecution of Spanish Jews. This culminated in the fifteenth century as the Spanish Inquisition spread outward into Portugal and Rome, and once again sent Jews running into their familiar diaspora pattern, pushing them deeper into Europe and the East. Still, they survived and even retained some of their haplotypic particularities. A group of Portuguese anthropologists recently discovered a small group of Jews living in the mountains of Portugal whose ancestors had apparently fled there and masqueraded as Catholics to escape th
e Inquisition.

  Despite what he and other geneticists have discovered, Ostrer is wary of saying too much about the genetic basis for Jewish identity. This is an area of inquiry that is still evolving rapidly, and he’s quite willing to admit that some of his conclusions are simply “a guesstimate.” There is no single haplotype that unites all Jews—instead, he and his team found four distinct haplotypes identified with different Jewish diaspora groups. There will never be a genetic “Jew or Not” test. All that Ostrer’s work reveals is that a genetically identifiable “Jewish people” survived the diaspora. We now have both historical and genetic evidence that scattering and hiding out during times of upheaval is a good way to ensure that your progeny will survive—even for dozens of generations.

  The Black Atlantic

  Toward the end of my conversation with Ostrer, we started talking about Jews today. We’re in the midst of another period of Jewish assimilation and migration, he said, making a sweeping gesture with his hands as if to encompass all of New York, or possibly the world. In the wake of nineteenth-century pogroms and the twentieth-century Holocaust, many Jews were forced to scatter to new areas. And some, like Reform Jews in the United States, have started converting people to Judaism again. The result of all this movement and intermixing is a Jew like me. My mother was a Methodist who converted to Judaism before she married my Jewish father. I was raised Jewish, but who knows what kind of haplotype I have? More to the point, when we’re talking about the survival of a group over centuries, does it really matter whether I’m culturally Jewish or genetically Jewish or somewhere in between? After hundreds of years of diaspora, aren’t all survivors a little bit hybrid?

  This is exactly the question that people from many diaspora groups have raised over the past half century. Perhaps nowhere is the answer to it more beautifully expressed than in the book The Black Atlantic: Modernity and Double-Consciousness, by Guyanese-British scholar Paul Gilroy. While researching the often fragmented histories of blacks in England, Gilroy realized that he should reframe black identity as a hybrid experience that combines many cultures. To describe the origin of this experience, he called on the idea of a “black Atlantic,” the geographical region where African slaves were scattered in a forced diaspora across Europe and the Americas. Instead of having a single point of origin, like the lands around Jerusalem, Gilroy’s diaspora has many origins. And its survivors are genetic and cultural hybrids. But that doesn’t mean African identities have been extinguished in people outside Africa today. It has survived in a multitude of ways, though some of them might be unrecognizable to communities who lived in Africa half a millennium ago.

  As Ostrer put it, diaspora is about where you come from, but it is also about where you end up. Our journeys change us radically, but when we settle down again there is a continuity, a shared history that holds us together. Jews and Africans are not unique in this respect—many groups have maintained a sense of community through times of hardship and separation. Recent human history teaches us that your group has a better chance of surviving in the long term if you’re willing to divide into groups and go your separate ways to safety. But that doesn’t mean the past is lost. What makes a book like The Black Atlantic so important is Gilroy’s powerful assertion that even if your group is unwillingly torn apart and assimilated into other cultures, your progeny will remember where they came from even hundreds of years from now.

  The Passover ritual makes a similar assertion. It is a celebration of identity forged in diaspora, and a reminder that survival often means finding a new home. The difficult part, as we face an uncertain future, is how to understand the meaning of “a new home.” We may have to look very far afield to get our answers. In fact, one of the greatest stories of survival through adaptation does not come from humans at all. It comes from the humble blue-green algae, whose incredible history may also show us one possible path into the future.

  11. ADAPT: MEET THE TOUGHEST MICROBES IN THE WORLD

  YOU’VE PROBABLY CALLED it scum. But that slimy blue-green goo floating in ponds and on the ocean comes from a group of species so hardy that humanity’s fumbling attempts to adapt to our environments would be a joke to them. Well, it would be if these blobs of raw biological productivity had a mean sense of humor, or brains, or even mouths to laugh with. We’re talking about our old friend cyanobacteria, whom we met billions of years ago, in the first chapter of this book. At that time, it was busily unleashing enough oxygen to transform the composition of Earth’s atmosphere. Its subsequent 3.5-billion-year career as a life-form proves that this ancient breed of scum has gotten something fundamentally right. Cyano, as it is fondly known among scientists, evolved one of the planet’s greatest adaptations: photosynthesis, or the ability to convert light and water into chemical energy, releasing oxygen in the process.

  Cyano has also had a secondary career as a biological building block for other life-forms. About 600 million years ago, sometime before the first multicellular life appeared, cyano began forming symbiotic relationships with other organisms, slowly merging with them over the millennia. Eventually these early cyano evolved inside other cells to become chloroplasts, tiny organs (known as organelles) that handle photosynthesis for plant cells. Every plant on Earth is, in fact, the result of this merging process. You can think of chloroplasts as both engines and batteries for plant cells; photosynthesis creates forms of energy that plants can use immediately as well as store for later. Cyano’s great adaptation is so powerful that plants and even a few animals like sea anemones have survived by absorbing cyano and turning it into their own adaptation.

  Brett Neilan, a biologist at the University of New South Wales, has spent his life studying cyano among the ancient rocks of Australia’s coastline, and he thinks the secret to the algae’s success is simple. Cyano’s ancestors won the evolution game because they worked with what the Earth always had in good supply: sunshine, or some form of light, and water. Like most plants, cyano are called autotrophs, a word that means “self-feeding,” and refers to their ability to feed themselves without consuming other organisms. In a sense, cyano generate the food they consume. As a result, they can and do live everywhere. They’ve been found in Antarctica and in the boiling, acidic waters of Yellowstone’s geysers. Not only are they seemingly impervious to dramatic temperature changes, but they are virtually immune to famine as well. According to Neilan, cyano prevent themselves from starving in times of scarcity by storing extra nutrients like nitrogen in little sacs tucked inside their cellular walls. If these food caches are not enough, cyano can go into stasis. The microbes put themselves into a kind of suspended animation and can endure without food for years, waiting out droughts or other disasters that affect their food supply.

  Cyano have other incredible abilities, too. They can live as individual single-celled organisms, but they can also join together with other cyano, Mighty Morphin Power Rangers–style, to form a multicellular creature. They are the simplest organism on Earth whose biological processes are regulated by the circadian rhythms of light and dark. Like humans, with our sleeping and waking cycles, cyanobacteria engage in different metabolic activities depending on whether it’s day or night. This allows them to engage in two separate chemical processes for nourishment—photosynthesis and nitrogen fixation—which would normally interfere with each other. Thanks to their circadian clocks, cyano can do photosynthesis by day and nitrogen fixation by night. They thus benefit from two kinds of nutrient production. Other plants benefit, too. Just as some organisms absorbed cyano to create choloroplasts, others have formed symbiotic relationships with the bacteria to reap the benefits of the energy produced by nitrogen fixation.

  Cyano have succeeded so well on Earth because they create their own food, using a power source that is ubiquitous and sustainable. It’s such a good strategy that other life-forms learned from cyano’s success millions of years ago and absorbed these tiny engines into their own fuel-production processes. Humans may not be able to merge with cyano on a bio
logical level—at least, not with current levels of technology—but many scientists are working on ways we could use photosynthesis to create more sustainable energy sources to help humans survive as a mass society.

  Why Is Photosynthesis So Awesome?

  One of these scientists is physicist-turned-biologist Himadri Pakrasi, who runs Washington University’s International Center for Advanced Renewable Energy and Sustainability (I-CARES). With a thatch of curly black hair just beginning to turn gray and a ready smile, Pakrasi radiates enthusiasm for his work. The first time I spoke to him, by phone, it was to find out how his lab had managed to create energy using water, light, and bacteria. “You should come out here and see!” he exclaimed. Very few scientists would invite a writer they’d never met before to visit their labs, but Pakrasi is the kind of guy who wants to get people engaged with his work—even strangers from halfway across the country. It was easy for me to understand how he’d built up a large international group of collaborators at Washington University, including scientists, city planners, and engineers.