The Invisible History of the Human Race (2 page)

As of 2014 there are still no artificially produced human clones, at least none that we know of, and journalists have long since stopped asking people if they want to be cloned. Many well-known animal clones, like Dolly the sheep and the resurrected “extinct” ibex, have died (some prematurely, some horribly). Other cloned animals, like Copycat, the world’s first cloned pet (born in 2001), are doing well. (The company that created Copycat, however, is no longer in existence.) In 2013, for the first time ever, a mouse was cloned from only a single drop of blood. In 2014 a Korean company called Sooam Biotech announced the birth of a dachshund clone called Mini Winnie, which it had created for a British woman who won a competition.

If our turn-of-the-century conviction that a race of more “us”es was imminent has proved to be as goofily off-kilter as our 1950s expectation that by now everyone’s car would fly, one of the more interesting consequences of this obsession was learning why the idea doesn’t actually work very well. We now know that if you took a person’s genome and tried to grow another human being from it, the resulting person would, of course, have much in common with the first, but he would be different as well. This is because while you can, at least theoretically, replicate a genome, you cannot replicate the precise conditions in which it developed. Genes respond to the environment around them. They get turned on and off by experience, and any one person’s life experience is as unique as our mothers once told us it was. Even identical twins raised in the same household can differ in height, facial features, or any number of traits. Typically the older identical twins get—that is, the more life experience they have—the more different they look too.

As far as science is concerned, it’s not just our unique lives that make true clones impossible; it’s the myriad unpredictable, unreplicable, and in some ways unknowable elements of a life that may trigger a genetic response. How could we quantify the factors that may affect a single gene in a year? How could we replicate the exact sequence and number of factors that shape one person’s genome in a lifetime? What, for example, was the impact on your genome of that unseasonably hot summer when you were eight? What about that traumatic encounter when you were ten? What was the effect of all that bread you ate at school, which was made from that particular wheat, which was imported from another country and which itself had an irreducible, hard-to-recapture life history?

Still, the iconic life of genes—their ubiquitous media presence, the casual way we attribute everything physical or emotional to them or specifically not to them, the intense attention they receive in the booming literature of parenthood, their telltale traces at crime scenes, and their Rosetta stone–like status in the science of being human—has grown.

 • • • 

CB and I pick up the glasses of salt water and swill it in our mouths. We are supposed to sluice it for thirty seconds, but the strong taste, combined with the sudden abundance of my spit, makes it hard to hold in. The saline collects cells from our mouths and as it does, the salt weakens the cell walls. Finally we spit it out into the green liquid, which is three parts water and one part detergent. “The cells of your body are like balloons,” says CB. “And there’s another little balloon inside them, which is called a nucleus. The detergent bursts the big balloon, and then it bursts the nucleus too, and then your DNA floats out.”

He holds up a glass of saline. “Do you guys want to do it?”

N. is romantic. “Is that what the ocean tastes like?”

F. is unmoved. “No. I’m not doing it. I’m never doing it!”

I offer him two dollars. He swills the saline.

Once the boys have spit out their own saline-plus-cells, CB and I carefully stir the new mixture. It’s still green but foggy, and a white foam layer has formed on top. Now the salt and detergent are breaking apart the cells and nuclei. Next we gently add the gin, letting it fall smoothly onto the back of a teaspoon and into the glass. It creates a new clear layer between the green and the foam. Because DNA does not dissolve in alcohol, the idea of this stage is to separate the DNA from the other bits of cell that are floating in the solution. Then we wait as, slowly, small white clumps appear, then a spidery line forms on the surface of my liquid. For one soaring second, we are all riveted to the same spot, thinking exactly the same thought:
That’s it!

We sit there poking at the fluid, swirling it around and watching as the clumps are pulled along, strand by strand. Inside each fragment is part of a code that has many more bits of information than stars you can see in the sky. These bits—scientists now say—have the potential to not just map tens of thousands of years of human genetic history but also to drop a small pin at the coordinates where our own DNA is located in it. And here, contained in these four glasses, is the genetic code for my entire family, my beautiful boys, who according to their DNA are not only mine: Half the stuff in their glasses came from me and half from CB, but it also all came
through
us. They are the children of a lineage, and inside the clumps that wander in their soapy water are organized pairs of amino acids that were arranged long before they or I was born—the result of thousands of generations shuffling their DNA.

 • • • 

Can our own personal DNA tell us about the history of the world? Isn’t that a bit presumptuous? For most of us, big history is not personal but something out there that we are enjoined to learn, a stack of snapshots of people and things that have been officially declared important.

On top of the pile is everything we think of as modern. Here are an iPhone and a Prius. Here’s the conflict in Syria. Here’s patient zero with H1N1. Underneath these photos are shots of the glamorous hairstyles, world events, and technological absurdities of the previous decades—here’s a cell phone the size of your sneaker, a computer the size of your house.

Further down are images from the nineteenth and eighteenth centuries: industry, ocean voyages, the beginning of journalism. Before these are images of a wonderful time called the Renaissance, when everyone painted and sculpted. Under them there are pictures of the Middle Ages, when peasants wore a lot of burlap and carried a lot of disease.

Prior to the peasants are the Vikings (helmets with nose guards, boats with many oars). They follow grimy snaps of the Dark Ages (muddier burlap, even more terrifying diseases). The pictures of the Romans (roads, plumbing, orgies) come before those of the Vikings, though they follow those of the Greeks (gods, columns, statues). There are a few pictures of biblical times (sand, camels, sun). They sit on top of a long reign of Egyptians (pyramids, mummies, cats).

By the time you get to the mummies, the pile is much shorter. Here are images of a long and undistinguished period of general barbarism, when people wore pelts and carried weapons. Down closer to the bottom of the pile are fuzzy pictures of the Stone Age (stones, scraggly hair, cave drawings), and below these only a handful of pictures remain.

These pictures are so dark you can barely make anything out in them at all. Here’s a cave. Here’s some ocher. Here, at the bottom of the stack, is a creature that looks a lot like a chimpanzee.

It’s fine to carry around these discrete snapshots, but it’s worth considering that history is continuous. We can track our way back through it by following the records we create, the writing that goes back six thousand years and the drawing that goes back forty thousand years. We can track our way back with oral histories, rumors, and stories that get passed down. Now, we can also track back through it with the longest thread of all, DNA.

 • • • 

Why do we care about where, or rather whom, we come from? Is it because of what is passed down to us from previous generations? Do the lives of our forebears impact ours in some way? Or is that just a story we like to tell ourselves? Within our families we have many convictions about traits, inheritance, and the mysteries of familial resemblance—she has her father’s nose; he has his grandfather’s cheeky sense of humor; those two are like peas in a pod. But what is real and what is myth? What do we actually know?

Over the years I’ve come to view the silence in my own family about my father’s father as an actual thing, not as the absence of something. I can see that the secret of his birth had a huge impact on his life, and I suspect it has on mine as well. And what of the man behind the secret? Did he leave anything more significant than the loud bang of a door shut down the generations? About 25 percent of my DNA comes from him. How has it shaped me?

This question led me to a few thousand more questions, which in turn eventually led me toward this book.
The Invisible History of the Human Race
became a personal quest to track down people from all over the world who could shine light on the package of things that gets passed down to us from our ancestors. As it turns out, the package is brimming: stories and secrets, names and dates, feelings, ideas and decision-making tools, and DNA. And that was merely the beginning. What makes the material that gets passed down in both our minds and our bodies so fundamentally interesting is how it shapes our lives, our identities, and our futures.

It was only after I began my quest that I stumbled across the idea of path dependency, a concept invented by physicists to explain how machines could most efficiently use energy to do their work. Path dependency was taken up to fascinating effect by economists to explain how what happens in the future may depend on the path that was taken from the past to the present. They used it to explain why some economies are healthier than others, why some laws are written the way they are, and why technology looks like it does in different places. When we talk about positive or negative spirals in our lives, when something that is good keeps getting better, or when something that is bad feeds back on itself and gets worse, we are talking about patterns that are path dependent.

The QWERTY keyboard is the classic example of path dependency in technology. Of all the keyboard setups that competed to become the standard in the era of the typewriter, QWERTY, for some godforsaken reason, won. Despite the fact that it was not the easiest or the best design for human hands, millions of people ended up using it, and eventually it became so firmly established that it was impossible to revise it. People were committed, and that commitment meant that nearly all laptops and keyboard are today laid out in
the QWERTY design.

When I came across the notion of path dependency, I realized like a thunderclap that this book was actually about how path dependency affects people in both their minds and their bodies. Path dependency is, of course, another way of talking about evolution, in that nothing ever evolves completely from out of the blue. The process is fundamentally stepwise: Evolution builds on what came before. The shapes of our bodies and our brains, for example, are constrained by the forms that they took in our ancestors. It’s no accident that we look like chimpanzees, because humans and chimpanzees shared an ancestor more than five million years ago.

The question that came to concern me, and that lies at the heart of this book, is how many of our decisions, and how much of our self-knowledge, are ultimately path dependent. The only way to find that out, of course, is to pause, turn around, and look back at all the paths the human race has taken. Ideally that would involve reconstructing some of the significant paths that have led to us to the present—where they began, who traveled along them, where they gently curved, and where they turned more sharply. As the saying goes, it’s not really the destination that matters but the journey you take to get there.

Since we are asking what is passed down, we have to ask who is doing the passing. Was it our parents, our society, our government? Has something been passed down incidentally or with purpose? Is the transmission complete or partial? And what do we believe about what we are passing down as we pass it down? Can we even
see
what we are passing down? In the case of culture, we generally believe we can. In the case of DNA, the answer for most of human history has been no.

Still, if you have ever wondered what has been passed down to you, if you have wondered, as I have, how much the past really does matter, you are particularly fortunate to be alive at the present moment. Because all the tools that we need to gaze back at the past—the records we have created, the abstract legacies of culture, and the visibility of DNA—have been radically transformed in the last ten years.

The massive digitization of paper records has completely changed the way we access and use them and, more important, what they can tell us. Additionally, and partly because of the utility of these new digital systems, some canny researchers have worked out how to measure the impact of distant historical events on the attitudes of communities today.

And then, of course, there’s DNA, nature’s digital record. Much of our general interest in DNA over the past few decades has been in genes and how they affect our health and determine our physical features. But as we got to know the genome better, it turned out that DNA has as much to do with our past as it does with our future. We learned that most of the genome is not coding DNA—that is, genes that express proteins
,
which then carry out some function in our bodies—but rather noncoding DNA, or what used to be called junk DNA. We now know that even if its impact isn’t direct, noncoding DNA may influence our genes in significant ways—or it may do nothing very obvious at all. But even in the latter case, as a group of brilliant scientists has shown, we may learn how to read the book of our history in it.

The most remarkable thing about the use of DNA as a historical tool is that it illuminates not just the biological past but the social past as well. As people make people, who make more people, they pass down their genes and an enormous quantity of noncoding DNA, and in all of this DNA we can trace the choices of populations, as well as fateful personal encounters, that took place thousands of years ago. So, although we have debated for years about the ways in which DNA shapes society (is it deterministic? is it indifferent? does it shape intelligence, behavior, race?), it is far more obviously the case that society shapes DNA.