PROLOGUE The worst scares of my life have usually come in unfamiliar places. I still panic a bit when I remember traveling into a Sumatran jungle only to discover my brother, Ben, had dengue fever. I lose a bit of breath any time I think about a night in Bujumbura when a friend and I got mugged. My fingers still curl when I recall a fossil-mad paleontologist leading me to the slick mossy edge of a Newfoundland cliff in search of Precambrian life. But the greatest scare of all, the one that made the world suddenly unfamiliar, swept over me while I was sitting with my wife, Grace, in the comfort of an obstetrician''s office. Grace was pregnant with our first child, and our obstetrician had insisted we meet with a genetics counselor. We didn''t see the point. We felt untroubled in being carried along into the future, wherever we might end up.
We knew Grace had a second heartbeat inside her, a healthy one, and that seemed enough to know. We didn''t even want to find out if the baby was a girl or a boy. We would just debate names in two columns: Liam or Henry, Charlotte or Catherine. Still, our doctor insisted. And so one afternoon we went to an office in lower Manhattan, where we sat down with a middle-aged woman, perhaps a decade older than us. She was cheerful and clear, talking about our child''s health beyond what the thrum of a heartbeat could tell us. We were politely cool, wanting to end this appointment as soon as possible. We had already talked about the risks we faced starting a family in our thirties, the climbing odds that our children might have Down syndrome.
We agreed that we''d deal with whatever challenges our child faced. I felt proud of my commitment. But now, when I look back at my younger self, I''m not so impressed. I didn''t know anything at the time about what it''s actually like raising a child with Down syndrome. A few years later, I would get to know some parents who were doing just that. Through them, I would get a glimpse of that life: of round after round of heart surgeries, of the struggle to teach children how to behave with outsiders, of the worries about a child''s future after one''s own death. But as we sat that day with our genetics counselor, I was still blithe, still confident. The counselor could tell we didn''t want to be there, but she managed to keep the conversation alive.
Down syndrome was not the only thing expectant parents should think about, she said. It was possible that the two of us carried genetic variations that we could pass down to our child, causing other disorders. The counselor took out a piece of paper and drew a family tree, to show us how genes were inherited. "You don''t have to explain all that to us," I assured her. After all, I wrote about things like genes for a living. I didn''t need a high school lecture. "Well, let me ask you a little about your family," she replied. It was 2001.
A few months beforehand, two geneticists had come to the White House to stand next to President Bill Clinton for an announcement. "We are here to celebrate the completion of the first survey of the entire human genome," Clinton said. "Without a doubt, this is the most important, most wondrous map ever produced by humankind." The "entire human genome" that Clinton was hailing didn''t come from any single person on Earth. It was an error-ridden draft, a collage of genetic material pieced together from a mix of people. And it had cost $3 billion. Rough as it was, however, its completion was a milestone in the history of science. A rough map is far better than no map at all.
Scientists began to compare the human genome to the genomes of other species, in order to learn on a molecular level how we evolved from common ancestors. They could examine the twenty thousand-odd genes that encode human proteins, one at a time, to learn about how they helped make a human and how they helped make us sick. In 2001, Grace and I couldn''t expect to see the genome of our child, to examine in fine detail how our DNA combined into a new person. We might as well have imagined buying a nuclear submarine. Instead, our genetics counselor performed a kind of verbal genome sequencing. She asked us about our families. The stories we told her gave her hints about whether mutations lurked in our chromosomes that might mix into dangerous possibilities in our child. Grace''s story was quick: Irish, through and through.
Her ancestors had arrived in the United States in the early twentieth century, from Galway on one side, Kerry and Derry on the other. My story, as far as I understood it, was a muddle. My father was Jewish, and his family had come from eastern Europe in the late 1800s. Since Zimmer was German, I assumed he must have some German ancestry, too. My mother''s family was mostly English with some German mixed in, and possibly some Irish--although a bizarre family story clattered down through the generations that our ancestor who claimed to be Irish was actually Welsh, because no one would want to admit to being Welsh. Oh, I added, someone on my mother''s side of the family had definitely come over on the Mayflower . I was under the impression that he fell off the ship and had to get fished out of the Atlantic. As I spoke, I could sense my smugness dissolving at its margins.
What did I really know about the people who had come before me? I could barely remember their names. How could I know anything about what I had inherited from them? Our counselor explained that my Jewish ancestry might raise the possibility of Tay-Sachs disease, a nerve-destroying disorder caused by inheriting two mutant copies of a gene called HEXA. The fact that my mother wasn''t Jewish lowered the odds that I had the mutation. And even if I did, Grace''s Irish ancestry probably meant we had nothing to worry about. The more we talked about our genes, the more alien they felt to me. My mutations seemed to flicker in my DNA like red warning lights. Maybe one of the lights was on a copy of my HEXA gene. Maybe I had others in genes that scientists had yet to name, but could still wreak havoc on our child.
I had willingly become a conduit for heredity, allowing the biological past to make its way into the future. And yet I had no idea of what I was passing on. Our counselor kept trying to flush out clues. Did any relatives die of cancer? What kind? How old were they? Anyone have a stroke? I tried to build a medical pedigree for her, but all I could recall were secondhand stories. I recalled William Zimmer, my father''s father, who died in his forties from a heart attack--I think a heart attack? But didn''t an old cousin once tell me about rumors of overwork and despair? His wife, my grandmother, died of some kind of cancer, I knew. Was it her ovaries, or her lymph nodes? She had died years before I was born, and no one had wanted to burden me as a child with the oncological particulars. How, I wondered, could someone like me, with so little grasp of his own heredity, be permitted to have a child? It was then, in a panic, that I recalled an uncle I had never met. I didn''t even know he existed until I was a teenager.
One day my mother told me about her brother, Harry, how she would visit Harry''s crib every morning to say hello. One morning, the crib was empty. The story left me flummoxed, outraged. It wouldn''t be until I was much older that I''d appreciate how doctors in the 1950s ordered parents to put children like Harry in a home and move on with their lives. I had no grasp of the awkward shame that would make those children all the more invisible. I tried to describe Uncle Harry to our genetics counselor, but I might as well have tried sketching a ghost. As I blathered on, I convinced myself that our child was in danger. Whatever Harry had inherited from our ancestors had traveled silently into me.
And from me it had traveled to my child, in whom it would cause some sort of disaster. The counselor didn''t look worried as I spoke. That irritated me. She asked me if I knew anything about Harry''s condition. Was it fragile X? What did his hands and feet look like? I had no answers. I had never met him. I had never even tried to track him down. I suppose I had been frightened of him gazing at me as he would at any stranger.
We might share some DNA, but did we share anything that really mattered? "Well," the counselor said calmly, "fragile X is carried on the X chro- mosome. So we don''t have to worry about that." Her calmness now looked to me like sheer incompetence. "How can you be so sure?" I asked. "We would know," she assured me. "How would we know?" I demanded. The counselor smiled with the steadiness of a diplomat meeting a dictator. "You''d be severely retarded," she said.
She started to draw again, just to make sure I understood what she was saying. Women have two X chromosomes, she explained, and men have one X and one Y. A woman with a fragile X mutation on one copy of her X chromosome will be healthy, because her other X chromosome can compensate. Men have no backup. If I carried the mutation, it would have been obvious from when I was a baby. I listened to the rest of her lesson without interrupting. A few months later, Grace gave birth to our child, a girl as it turned out. We named her Charlotte.
When I carried her out of the hospital in a baby seat, I couldn''t believe that we were being entrusted with this life. She didn''t display any sign of a hereditary disease. She grew and thrived. I looked for heredity''s prints on Charlotte''s clay. I inspected her face, aligning photos of her with snapshots of Grace as a baby. Sometimes I thought I.