Photo credit: Mistina Hanscom
How did you first become interested in the topic of heredity?
I’ve been fascinated by heredity for as long as I can remember, but I think all of us are. As a science writer, I have to explain what meiosis
is, but I don’t have to define heredity. We all wonder about our ancestors — who they were, how they lived, and how countless generations of lives came together to produce us. We compare children to their parents and their grandparents, searching for what they inherited — not just their eye color, but their height, their personality, and every other imaginable trait.
But when my wife was pregnant with our first child, heredity became a matter of urgency. What would my child inherit from me, I wondered? And how would that inheritance get carried down to future generations? As a journalist, I’ve reported for The New York Times
about a lot of advances in our scientific understanding of heredity in recent years. One day I decided to dive deep into all that science and history, and — after a lot of work — I had written this book.
You write that we need to change the way we think about heredity. How do you define it? What are some of the most pervasive myths about heredity?
For centuries, people believed in the power of blood. People inherited their nature through blood — royal blood, noble blood, and so on. Curses were carried down in the blood, too. In the 1500s, the modern concept of race emerged, based again on the heredity of blood (hence the “one drop rule” for race in the United States).
We now know these concepts don’t make biological sense. We don’t inherit blood, but we do inherit genes. Yet we still talk about genes in the same way we talked about blood. I’ve heard friends talk about getting 23andMe tests, excited to discover that they have “Irish DNA.” They talk about it as if it explains how their lives have turned out.
An obsessive focus on genes also prevents us from seeing the other channels through which heredity can flow. When we teach children, we are passing down culture — which is no less important than the DNA they inherit. Microbes infect their hosts and get passed down through the generations. It’s possible that some molecules aside from DNA may get passed down from parents to children.
The best way to think about heredity is what the past gave the present, and what the present will pass down to the future.
You are the first journalist to get your genome sequenced and to explore it scientifically. You’ve even posted it online for scientists and students to analyze if they so wish. How did the results stack up to your expectations? Any advice for people who are considering genetic testing like AncestryDNA or 23andMe?
We think of our DNA as the book of life. If we just open it up, we can read our truest selves. But that’s not true. There are millions of tiny differences between my genome and yours, and scientists are only starting to figure out how those differences matter to our health, our personalities, and other aspects of our lives.
For example, 23andMe can tell you what percentage of your DNA comes from Neanderthals. That’s all well and good, but what really matters is which parts of your DNA come from them. Yet even if you can find out — as I did — the meaning of that inheritance still remains a mystery. I’ve discovered that my Neanderthal DNA is associated with a risk of bloody noses and toe deformities, for example. It’s hard to know what to make of that, given that my nose doesn’t bleed a lot. Also, my toes look pretty nice, if I do say so myself.
My advice for people who are thinking of getting AncestryDNA or 23andMe tests is to prepare both to be shocked and to be bored. If your test delivers information on genetic diseases, there’s a very small chance that you may find that you have a mutation that is a serious threat to your health. If your test doesn’t find any medical conditions, that doesn’t mean that you don’t have any harmful mutations. It only means that your particular test didn’t find any.
Some companies try to juice up their test results by telling you about traits that don’t have to do with disease. But these results can be underwhelming. When my wife took a 23andMe test, she learned that she is “likely” to have blue eyes. She has, in fact, a 100% chance of having blue eyes.
Genetic testing can also give clues about ancestry. Those results may tell you what you already knew — or give you a surprise. According to one analysis of my genome, I have a lot of southern European ancestry. That goes against a lot of genealogical research my relatives have done. So either their research is wrong, or there’s a big secret someone needs to explain to me. Or maybe the genetic test itself is wrong. These ancestry tests are still in their early days, and their results are crude. They depend entirely on how many people and populations a testing company compares you to.
As these companies add more people to their databases, they’re going to get better at determining people’s ancestry. And they are already very good at identifying close relatives. (An open-source DNA-sharing site already revealed the Golden State Killer’s relatives, for example, leading to his arrest.)
From time to time, people who use these tests are discovering that their families have been hiding some deep secrets. Again, this is not likely to happen, but you have to be ready for the small chance that it will.
Is it possible I’m related to Charlemagne or Cleopatra?
Yes, but I’m afraid it doesn’t make you special.
We envision our ancestors like infinitely dividing branches — two parents, four grandparents, eight great-grandparents, and so on. But if that were truly the case, then a few thousand years ago, your own ancestors would outnumber all the humans who ever lived. In fact, our ancestors are related to each other, joining those branches together. The shape of our family trees gives rise to some remarkable facts. Charlemagne is the direct ancestor of all living Europeans, for example. And Cleopatra may be a direct ancestor of all living humans.
What surprised you most during your research for the book?
Heredity is full of surprises — it just won’t follow our intuitions. For example, we assume that we inherit DNA from our ancestors. After all, in each generation genes get copied in and passed down to the next one.
But it’s not as simple as that. People carry two copies of each gene, inherited from each parent. When they have children of their own, each of those copies has only has a fifty-fifty chance of getting passed down. Repeat this selection over many generations, and something surprising happens: some people’s DNA disappears altogether from some lineages of their descendants.
Pick one of your ancestors from 10 generations back, scientists have found, and there’s about a fifty-fifty chance that you inherited none of their DNA. They’re still your ancestors, but you have no genetic connection.
You write that we humans have a form of heredity that no other species have. How is that possible?
Anthropologists are realizing that one of the most exceptional features of our species is our ability to teach each other. Even chimpanzees, our closest living relatives, don’t show any clear ability to teach. Teaching requires a lot of special adaptations in our brains — on the teacher’s side, the ability to know what students do and don’t understand, and on the student’s side, a bias to imitate people who seem to know a subject well.
This unique feature of our species lets us pass down culture from one generation to the next. Many social scientists now believe that this cultural heredity is responsible for our incredible success as a species. We passed down lessons about how to farm and construct buildings. In the process, we remade the planet. Now we have to alter our cultural heredity if we want to survive for centuries to come.
÷ ÷ ÷
writes the “Matter” column for The New York Times
, and has frequently contributed to magazines such as The Atlantic
, National Geographic, Wired
, and Scientific American
, among others. A frequent contributor to Radiolab
, he is the author of numerous books about science, including Microcosm
, Parasite Rex
, and She Has Her Mother's Laugh
. He has won numerous awards for his writing, including from the National Academy of Sciences and the American Association for the Advancement of Science. He is professor adjunct at Yale University.