A Brief History of Everyone Who Ever Lived: The Human Story Retold Through Our Genes
This is a story about you. It concerns the tale of who you are and how you came to be. It is your individual story, because the journey of life that alights at your existence is unique, as it is for every person who has ever drawn breath. And it’s also our collective story, because as an ambassador for the whole of our species, you are both typical and exceptional. Despite our differences, all humans are remarkably close relatives, and our family tree is pollarded, and tortuous, and not in the slightest bit like a tree. But we are the fruit thereof.
Something on the order of 107 billion modern humans have existed, though this number depends on when exactly you start counting. All of them—of us—are close cousins, because our species has a single African origin. We don’t quite have the language to describe what that really means. It doesn’t, for example, mean a single couple, a hypothetical Adam and Eve. We think of families and pedigrees and genealogies and ancestry, and we try to think of the deep past in the same way. Who were my ancestors? You might have a simple, traditional family structure or, one like mine, handsomely untidy, its tendrils jumbled like old wires in a drawer. But no matter which, everyone’s past becomes muddled sooner or later.
We all have two parents, and they had two parents, and all of them had two parents, and so on. Keep going like this all the way back to the last time England was invaded, and you’ll see that doubling each generation results in more people than have ever lived, by many billions. The truth is that our pedigrees fold in on themselves, the branches loop back and become nets, and all of us who have ever lived have done so enmeshed in a web of ancestry. We only have to go back a few dozen centuries to see that most of the 7 billion of us alive today are descended from a tiny handful of people, the population of a village.
History is the stuff that we have recorded. For thousands of years, we have painted, carved, written, and spoken the stories of our pasts and presents, in attempts to understand who we are and how we came to be. By consensus, history begins with writing. Before that we have prehistory—the stuff that happened before we wrote it down. For the sake of perspective, life has existed on Earth for about 3.9 billion years. The species Homo sapiens, of which you are a member, emerged a mere 300,000 years ago, as far as we know, in pockets in the east and north of Africa. Writing began about 6,000 years ago, in Mesopotamia, somewhere in what we now call the Middle East.
For comparison, the book you are holding is around 115,000 words, or 685,000 characters long, including spaces. If the length of time life has existed on Earth were represented as this book, each character, including spaces, is around 5,957 years. Anatomically modern humans’ tenure on Earth is equivalent to
. . . the precise length of this phrase.
The time we have been recording history is an evolutionary wing-flap equivalent to a single character, the width of this period<.>
And how sparse that history is! Documents vanish, dissolve, decompose. They are washed away by the weather, or consumed by insects and bacteria, or destroyed, hidden, obfuscated, or revised. That is before we address the subjectivity of the historical record. We can’t agree definitively on what happened in the last decade. Newspapers record stories with biases firmly in place. Cameras record images curated by people and only see what passes through the lens, frequently without context. Humans themselves are terribly unreliable witnesses to objective reality. We fumble.
The precise details of the events of September 11, 2001, when the World Trade Center towers were destroyed, may well remain obscure because of conflicting reports and the chaos of those horrors. Witness testimonies in courts are notoriously defective and are always subject to squint-eye scrutiny. Flit back a few centuries, and there is no contemporary evidence even for the existence of Jesus Christ, arguably the most influential man in history. Most of our tales about his life were written in the decades after his death by people who had never met him. Today, we would seriously question that, if it were presented as historical evidence. Even the accounts that Christians rely on, the Gospels, are inconsistent and have irreversibly mutated over time.
This is not to disparage the study of history (nor Christianity). It’s merely a comment on how the past is foggy. Until recently it was recorded primarily in religious texts, business transaction documents, and the papers of royal lineages. In modern times we have the opposite problem—far too much information and almost no way to curate it. In every purchase you make online, every Internet search you do, you volunteer information about yourself to be captured by companies in the ether. Books, sagas, oral histories, inscriptions, archaeology, the Internet, databases, film, radio, hard drives, tape. We piece together these bits and bytes of information to reconstruct the past. And now, biology has become part of that formidable swill of information.
The epigraph at the beginning of this introduction is Darwin’s single reference to humans in On the Origin of Species, right at the end, as if to tease us that there will be a sequel. With his proposed theory of descent with modification in the distant future, light will be shed on our own story: to be continued.
That time has come. There is now another way to read our pasts, and floodlights are being shone on our origins. You carry an epic poem in your cells. It’s an incomparable, sprawling, unique, meandering saga. About a decade ago, fifty years after the discovery of the double helix, our ability to read DNA had improved to the degree that it was transformed into a historical source, a text to pore over. Our genomes, genes, and DNA house a record of the journey that life on Earth has taken—4 billion years of error and trial that resulted in you. Your genome is the totality of your DNA, 3 billion letters of it, and due to the way it comes together—by the mysterious (from a biological point of view) business of sex—it is unique to you. Not only is this genetic fingerprint yours alone, it’s unlike any other of the 107 billion people who have ever lived. That applies even if you are an identical twin, whose genomes begin their existence indistinguishable, but inch away from each other moments after conception. In the words of Dr. Seuss:
Foreword by Siddhartha Mukherjee
Part One: How We Came to Be
1. Horny and mobile
2. The first European union
3. These American lands
4. When we were kings
Part Two: Who We Are Now
5. The end of race
6. The most wondrous map ever produced by humankind
8. A short introduction to the future of humankind
References and further reading
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