The Invisible History of the Human Race (27 page)

“I would have discounted her story pretty much out of hand as almost unprovable or almost unbelievable that a family could for twenty generations pass on that they were part of this minority group,” Greenspan told me. “I always worry when we deal with oral history without dealing with the DNA because I think that the difference between telling stories and telling truth is multiple sets of evidence.”

 • • • 

After fewer than fifteen years in business, personal genetics companies have made possible a genetic-based social networking that makes the social networks of the early 2010s look like child’s play. Customers of 23andMe, Family Tree DNA, and AncestryDNA can discover an extraordinary collection of genetic cousins and track not just their families but specific segments of DNA in their genome. By combining the records research of millions of people with the analysis of their DNA, users can build an actual copy of their human network over the last few hundred years or longer and find their individual place within it.

Companies alert customers when another customer has one or more largeish segments of DNA that look exactly the same. Geneticists say these shared segments have “identity by descent,” meaning they are the same because we got them from the same person. The implication is that the segment has been inherited by both customers from a common ancestor. Accordingly, the company will describe the DNA matches as a “relative” or a “cousin.” Fundamentally, the more closely related you are to someone, the more segments you will have in common, and the longer they will be.

It is said that autosomal DNA can take you back at least five generations. The probability of identifying a third cousin using autosomal DNA is roughly 90 percent, a fourth cousin 50 percent, and a fifth cousin 10 percent. Greenspan said he knows of people who have definitively identified eighth cousins with autosomal DNA. It’s hard to believe that these boundaries won’t be extended further as the science develops.

With a large enough group of descendants in a single family line, it is even possible to rebuild the genome of the dead. The genome of each living person could be used as a virtual puzzle piece with which to reassemble much of the genome of the group’s common ancestor. It is theoretically possible, though no one has yet done it, to reconstruct individuals who have left no trace in written history at all. “With enough people,” Woodward said, “you could project back and rebuild the population of Leigh in Lancashire, England, in 1850.”

A few years ago Blaine Bettinger, an intellectual-property lawyer with a background in molecular biology, began a personal search for the DNA of his great-grandmother. Born in 1889, she lived so long that Bettinger, who is thirty-eight, met her as child. She was adopted, he said, so he knew nothing about her genetic background. Yet she was “
an incredibly strong woman who had a big impact.” There are traits in Bettinger’s family—he thinks of them as ripples—that seem to emanate from her. In order to explore her and her influence on his family, Bettinger started collecting the DNA of her descendants so that he could isolate some of what they inherited from her.

With the help of two of her grandchildren, he has been able to identify thirty-five segments of DNA spread over almost every chromosome that came from her
and
her husband. His next step is to find relatives who match through those isolated segments so that he can prize apart which segment came from her and which came from him. As well as convincing members of his family to participate, Bettinger uses cousin matching to find others who overlap on those segments.

Wading through the personal-genomics options and analyses can be daunting for people who have not thought much about their own genes before. Bettinger ordered his first DNA test in 2003, when companies offered to read around 175 markers on the autosome; now the tests examine just under 1,000,000 markers. As a result, Bettinger has become a leader in the genetic genealogist community, part of a select group of individuals who help people understand their cousin networks and what their DNA may tell them, much of it through his popular blog, TheGeneticGenealogist.com.

CeCe Moore, another genetic genealogist and blogger (YourGeneticGenealogist.com), became interested in the subject when she began to put together a family tree for a niece who was getting married. “
Little did I know, it’s addicting,” she said. “And I’m one of those obsessive-compulsive types.” Moore used to work as a TV producer but is now a genetic genealogy consultant for the television shows
Finding Your Roots
, with Henry Louis Gates Jr. and
Genealogy Roadshow
. She has essentially developed an entirely new class of career, not just explaining and interpreting the ins and outs of DNA but being a genetic detective who helps clients find the missing. Now she eats, lives, and breathes DNA all day, she said, and often through the night as well.

One of the growing uses of genetic genealogy is for adoptees to find families, and Moore, who is the administrator of the Adopted DNA Project at Family Tree DNA, is regularly asked for help. “I get e-mails from people literally every day who found out they’re not who they thought they were genetically,” she said. “They come out as a half-sibling to their sibling, who they thought was their full sibling. This is happening all the time. It usually turns out that the father isn’t the father. I’ve also been contacted about what looks like a baby switch in the hospital.” One of Moore’s earlier cases involved tracking the family of someone who was left on a doorstep in 1916, but in the past year she has been contacted on behalf of half a dozen individuals who were abandoned as newborns, some found in dumpsters.

Sometimes people don’t get the ancestral result that they expect. They assume that they are Irish, but the test says their DNA is more like that of a Russian Jew. “This is just my experience,” Moore added. “It could be that people are drawn to testing who always felt like they didn’t fit in or always had a question in their mind, but the numbers are very high.”

By starting with the segments of DNA that people have in common on one or more chromosomes in genetic genealogy databases, Moore has found missing siblings and even parents. First she tracks back through the family histories of the genetic cousins to find a common ancestor among them, then she will attempt to work her way down again from the common ancestor to find the individual’s parents. “You build the tree up and then you build the tree down,” she said. “If a predicted second cousin shares great-grandparents with a person looking for their birth family (maybe great-great-grandparents, if they just happen to share a little more DNA than expected), we can build that tree down; we can see who lived in the right place at the right time, who was the right gender, and you can sometimes solve it.” Sometimes Moore has found a direct match, where it is quite obvious from the amount of DNA that two people have in common across many chromosomes that they are siblings or parent and child. She recommends that all her clients send their samples to 23andMe, Family Tree DNA, and AncestryDNA, which together have databases of over one million autosomes. “You have to fish in all three ponds.” Sometimes all that can be found about someone is her general ancestry: A recent client discovered that she was Mexican, which she had no idea was the case.

While many individual mysteries have been solved with genetic genealogy, if we change the focus to entire populations, shared chunks of autosomal DNA can take us much further back in time than even eight generations ago.

 • • • 

Modern culture is good at retaining general knowledge from the recent past, and since the invention of archaeology and paleoanthropology we’ve been able to recover some of the distant past too. Still, much of what we know about the ancients had to be effortfully uncovered. Though we may feel a kinship with figures from the nineteenth and eighteenth centuries or even the Picts, who lived a millennium ago, or the Romans from a thousand years before that, we have lost almost all sense of connection with most people who lived more than two thousand years ago. We have a reasonably good idea about some of their knowledge, which we’ve been able to work out from the traces they left. But we have little sense that that knowledge was passed on to us, not in the same way that we can confidently recognize the innovations and legacies of various significant characters over the last five hundred years, from Leonardo da Vinci to the Wright brothers.

Yet we are now on the cusp of boom times in deciphering the deep history of the world, because in addition to the commercial genetic genealogy companies, many scientific teams are devising different methods to get even further back into the past. They promise not only to illuminate chronologically and emotionally distant times but also to clarify the ways in which we remain connected to them. At the same time that the British team was devising a unique method for revealing the regional genetic blends of Britain, Peter Ralph, a professor of biology at the University of Southern California, and his colleague Graham Coop of the University of California at Davis were developing another way to dig into the history of Europe via its DNA. They examined the genomes of a group of 2,257 Europeans, divided into forty different populations, and identified all the small segments of DNA that any two people had inherited from a recent common ancestor. The goal was to understand the way people are related in modern-day Europe and, in the process, to learn how human
networks have changed through time.

Ralph and Coop found that any two modern Europeans who lived in neighboring populations shared between two and twelve genetic ancestors in the previous 1,500 years. These foreign cousins are a testament to the fundamental interconnectedness of all people but also to how ultimately disparate we are: Twelve genetic cousins in another country after 1,500 years isn’t exactly grounds for a family reunion. A similar study found that in a sample of five thousand Europeans, there were tens of thousands of pairs of
second to ninth cousins. According to Ralph and Coop, in the period between 1,500 and 2,500 years ago, a given pair of individuals would likely have shared one hundred or more genetic ancestors, which means they carried the same random segment of DNA passed down over all that time from an eightieth-grandparent—perhaps a Roman legionnaire, a Portuguese sailor, or a Greek shepherd. The farther apart people lived in Europe, the less likely it was that they shared genetic ancestors, although, say Ralph and Coop, they would still likely share some.

The way that genomes are cut, split, and shuffled across generations has significant consequences for their structure today. How do segments of DNA break apart and come back together again? I asked Ralph, who suggested that I re-create a lineage, at least on a tiny scale, to see how the process works. I returned to the kitchen table, and again sat there with my genome before me, only this time it was made of paper, a red strip to symbolize all the genetic material I received from my mother and a green strip to represent all the DNA I received from my father. I wanted to follow half of my DNA back through the generations, so I set the green paper aside, which left me with half my genome—everything I received from my mother.

I chopped the red strip into twenty-three smaller bits to represent the chromosomes in my cells that were made by my mother and then passed on to me. Then I passed the strips farther up the table, symbolically sending them back up the tree to my mother. In order to get a sense of what her genome looked like, I then added another twenty-three strips of brown paper to represent the DNA that my mother did not pass down to me.

The funny thing about the set of chromosomes before me was that even though I was looking at my mother’s total genetic material, I was not looking at her actual chromosomes. The chromosomes she gave to me underwent a process of recombination before she passed them on. Segments of DNA were swapped between each pair, so that overall her chromosomes broke and then recombined on average about thirty-two times across the genome.

In order to unscramble the process, I chopped up the forty-six red and brown strips and swapped pieces between them. This was finicky work, so I settled for doing it just thirty times, which meant that most of the forty-six resulting strips had at least one red segment and one brown segment. These twenty-three pairs of mosaic strips represented my mother’s actual chromosomes.

Because I wanted to follow my DNA back another generation to my mother’s mother, I did the same thing for her. I discarded one chromosome from each of my mother’s pairs, which left me with the twenty-three chromosomes she got from her mother. Again I pushed them a little farther up the table, back through time and to the spot in the tree where my maternal grandmother perched. Then I added twenty-three blue strips of paper to pair up with each of the chromosomes that my grandmother gave to my mother, to represent all the genetic material that my grandmother had but that was never passed down to my mother. In order to disassemble those twenty-three chromosome pairs and rebuild their original state in my grandmother’s cells, I chopped them up and painstakingly pushed tiny little pieces of paper between the strips into alignment with others.

Some of the motley strips that represented my grandmother’s original chromosomes had four different segments with three different colors. Because I was using specific colors to indicate where the DNA would end up, I could see which segments of my grandmother’s DNA came down through the generations to me, which went to my mother but not to me, and which were not replicated at all. If I continued to do this for one hundred generations, all the pieces of my personal genome would become smaller and smaller and be dispersed further and further
throughout my genealogical tree.

Yet as I dispersed and reconnected the chunks back through the time span of just a few generations, I could see they were not just different colors but also slightly different lengths. At first it was easy to divide the genomes up and push them back through the generations, but it wasn’t too long before the chunks reached a size where they were not divided at all. They moved from one generation to another without changing in size. This was what Ralph wanted me to see: It is often the case that these segments of DNA will be passed on
whole
to the next generation and then, still whole, to the next. It may be many generations before they are once more chopped down.