I imagine her Middle Passage. She cowers among other women in the hold of a ship as it pitches and rolls, light knifing through chinks in the vessel’s ribs, her naked body smeared with vomit and the tang of saltwater, stench of urine tickling her gag. All around her men are chained in bilboes, iron cuffs that pin them down, side by side, for weeks, months. Most mornings the Portuguese traders climb down for a corpse, lift the stiff, slender limbs onto the foredeck, where a few feet away whitecaps surge to receive their tribute. Years later she’ll regard this voyage as through a misted window, blurred forms and recollections evaporating beneath a harsh Southern sun as she works rows of tobacco, catching the gaze of an overseer or a master’s son.
My great-great-great-great- (or great-) grandmother.
Last fall I spit into a vial, sealed it within a small box, and dropped the package into the mailbox on my block in Brooklyn. I’d succumbed to the siren song of 23andMe.com, whose technology and algorithms would comb through my twenty-three pairs of chromosomes, teasing out strands of ancestry. On New Year’s Day I got an email alert that prompted me to log into the site — as expected, I was of 99% Northern European ancestry, mostly British and Irish but also sequences identified as French, German, Scandinavian, and even Finnish in origin. The real shocker, though, was that I’m 1% non-white: wisps of Native American and Middle Eastern DNA, and there, bright-red bands along chromosomes five and twelve, the imprint of a nameless West African woman.
Two new books probe this biological shuffle, how genome’s alphabet – the famous four letters, A, T, C, and G, repeated billions of times – shift and mutate with each cut of the deck, constantly recreating our common humanity, confirming some patterns and debunking others. A finalist for the National Book Critics’ Circle’s Nonfiction award, A Brief History of Everyone Who Ever Lived, by British geneticist and science writer Adam Rutherford, owes a debt to the groundbreaking research of Harvard’s David Reich, a leading scientist who analyzes ancient DNA, and author of Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past. Rutherford repeatedly cites Reich’s influence; and while there’s considerable overlap between the books, they skew apart in focus, complementing each other, revealing all the better how biology shapes us in an age of identity politics.
Reaching back into deep time, Rutherford and Reich explore admixture, how populations blend when they encounter each other. Both authors acknowledge the visionary Svante Pääbo, a Swedish biologist who sequenced the Neanderthal and Denisovan genomes, proving that early modern humans interbred with these other human species. (Pããbo’s own excellent if technical book, Neanderthal Man: In Search of Lost Genomes, depicts how his lab transformed the discipline of paleogenomics by inventing technologies and protocols to extract ancient human DNA from bone. It’s an impressive feat: only about 1% of ancient genetic material is human — the rest contamination from bacteria and even from the hands of scientists in the lab.)
A Brief History of Everyone Who Ever Lived is the more beautifully crafted book. An accomplished stylist in the mode of Ed Yong, Rutherford sprinkles wit and erudition throughout his narrative and footnotes, with playful chapter titles such as “Horny and Mobile,” subheads that allude to Dylan Thomas and Anne of Green Gables. It’s a captivating read, as Rutherford’s whimsy and intelligence guide the reader through labyrinthine science. When he plunges into weightier issues – what do genomic changes suggest about race, gender, and inequity? – he tends to focus on variation within populations, rather than between them. Any two random sub-Saharan Africans, for instance, will likely be more closely related to a similarly random Norwegian than to each other.
“Human variation is continuous wherever we look too, but unlike light, not in a single line,” he writes. “The Jews once had high (but not exclusively high) rates of Tay-Sachs disease. Now they do not. Some Jews have ginger hair and pale skin, just like plenty of Scots. Others do not. The skin tone of the people of the Andaman Islands is very similar to that of the people of central Africa, but they acquired that hue via different historical and biological routes. Some black Africans are evolved to process oxygen at high altitudes, as are some Tibetans, but most are not. ‘Black’ is no more a race than ‘long-distance runner’ is.”
Who We Are and How We Got Here is the drier but deeper work, brimming with graphs, maps, and timelines; Reich leaves no stone of data unturned. While his voice occasionally lapses into textbook jargon, which may tax the reader’s patience, he gives us as complete a genomic history of our species as one can find in 2018, with reams of original research, spanning from early Homo species to anatomically modern humans, who emerged around 300,000 years ago, to the dispersal of populations before and after the “Out of Africa” bottleneck around 50,000 years ago. Reich offers lush portraits of Neanderthals and Denisovans, “Mitochondrial Eve” and “Y-chromosomal Adam,” ghost populations, such as the Northern Eurasians, long gone but inferred from its contributions to both European and Native American DNA. He’s especially strong as he aligns his investigations with archeology and linguistics : as he moves from continent to continent, from Eurasia (which he views as a vital incubator of humanity) to India to East Asia and Australia to the Americas, and then circling back to Africa, he evokes a grand, wondrous narrative: the staggering genetic variation among Eurasian and African populations, how caste has tinkered with Indian genes, the budding of so many Native American groups and languages from a single founder population. The history of Homo sapiens pieces together like a gorgeous mosaic . . . until it doesn’t, as in the perplexing New Guinean genome, or the traces of a vanished people who arrived in the Amazon basin long before Native Americans.
Most of our current genomic makeup was mapped around 10,000 years ago, catalyzed by the advent of agriculture, and yet taking centuries to spread. My personal ancestry is rooted in the British Isles; and yet the builders of Stonehenge 6,000 years ago looked nothing like me, as they were subsequently erased by the fair-skinned Yamnaya, nomads whose DNA blazed from the Russian steppes into niches around the world. As Reich emphasizes, the Homo sapiens family tree is more an intricate trellis of vines, branching away and then weaving together: “There was never a single trunk population in the human past. It has been mixtures all the way down.”
Reich saves the most provocative arguments for his conclusion. As more paleogenomes come online – because of legal and cultural prohibitions, we currently have black holes in ancient DNA from China and indigenous people of North America — the future of the past will surely unveil biological differences among groups, challenging fixed notions about race and gender, inequality and power. Reich highlights clusters of DNA associated with what we consider “race” (although he shrugs off that term as crude and imprecise, weighed down by historical baggage). His prose grows richer, more philosophical: “The genomic evidence of the antiquity of inequality – between men and women, and between people of the same sex but with greater and lesser power – is sobering in the light of inequality today . . . Constant efforts to struggle against our demons – against the social and behavioral habits that are built into our biology – is one of the ennobling behaviors of which we humans as a species are capable, and which has been critical to many of our triumphs and achievements.”
Perhaps the most crucial thread that links Rutherford and Reich is their contagious passion for humanity’s story, how quantum leaps in the study of ancient DNA has yielded surprise after surprise, adding mystery to revelation. We all contain multitudes of peoples, from prehistoric Irish kings — whose Y chromosome I share with Henry Louis Gates and millions of other men — to a terrified young woman stolen from her homeland and condemned to unspeakable agonies in a strange land across a vast ocean.