Carl Zimmer is the author of the new book She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity. His other books include A Planet of Viruses and Parasite Rex. He is a columnist for The New York Times and a professor adjunct at Yale University.
Q: What was the inspiration for your new book?
A: I was looking back over some of the articles I’ve written, and I noticed a pattern of writing about different aspects of heredity. I asked myself why I was so interested in it---I have two teenage kids, and maybe it’s something growing on my mind.
I decided to do broader research on the history of heredity. I decided it would be my next book. It’s so fascinating. It’s important for our identity, our culture, and scientists are delving into heredity more and more deeply.
Q: What did you learn about your own genetic makeup from working on the book?
A: I learned that I probably have a genome a lot like other people’s genome, and that’s fine. There’s nothing that makes it exceptional. But if you prowl around in your genome, you will find something. I have a variant that protects me from various autoimmune diseases. Scientists have developed a drug to treat these autoimmune diseases.
I was able to pinpoint my Neanderthal genes. It’s fascinating but perplexing. It’s hard to tell what they mean for you. I have one that’s associated with nosebleeds—I never thought of myself as someone with many nosebleeds. And why would Neanderthals be prone to nosebleeds?
A lot is still mysterious about our genome. We have given them names but [don’t know much about them].
Q: You examine a variety of traits in the book, one of which is the inheritance of intelligence. What did you learn about that?
A: The history of intelligence and heredity is filled with a lot of horrors. It’s been used to justify sterilization and to justify lifelong institutionalization, and in Nazi Germany to justify mass murder.
We have to keep that history in our minds constantly. Why is it so easy for people to make claims about intelligence and use it to make awful social policy?
At the same time, intelligence is not just a social construct. It’s a real psychological feature of the mind. It’s something you can measure. Intelligence test scores are linked to how likely [people] are to be alive at 79 years old.
We have to accept this overwhelming research on intelligence. On top of that, we know the variation in test scores is influenced by genes we inherit from our parents. They don’t determine it, but it is an influence.
Scientists are discovering more and more genes. It’s going to lead to exciting research on how our brains work. It might lead to interesting educational programs.
But at the same time, we can’t take these insights and use them to justify biases against certain groups of people. It’s easy to do so, but it’s wrong.
There’s a correlation between IQ and heart disease—we don’t understand why it’s there, but it’s there. Maybe genes that influence intelligence test scores influence how the heart functions. We don’t know. It could help come up with ways for people to live longer.
Q: Another issue you look at is the inheritance of height. Can you say more about that?
A: In the book I spend a lot of time talking about height and intelligence because there are some amazing parallels. You don’t think of height as being like intelligence. Intelligence is very controversial and height is just how tall you are.
But height and intelligence are actually two of the big questions about heredity that drove the whole science of heredity in the mid-1800s. Scientists such as Francis Galton would look at people and say that it seems tall parents have tall children.
Where it’s very difficult to measure intelligence—it took decades to come up with reliable tests—measuring height was easy.
The first important thing they did was look at twins. Identical twins tend to be closer in height than fraternal twins or siblings. We knew height was very heritable—the genes have a really strong influence—but it wasn’t until 2007 that scientists discovered the first gene that had a clear-cut influence on a broad range of people with height. If you have it, you’re ¼ inch taller.
Since then, scientists have discovered over 3,000 genes, revealing that something as simple as height is an incredible web of influences we inherit. Maybe all our genes influence our height.
And yet even with the influence from genes, it doesn’t mean we should assume heredity completely determines what our height will be. We are taller than our predecessors 100 years ago. There’s been a steady increase in height. With the same DNA, if kids get better food, medicine, sanitation, it will stimulate their bodies to get taller. It’s a sign in some ways the planet is getting healthier.
Intelligence has the same paradox—genes matter but so does environment, and IQ scores are increasing. Compare IQ scores from 100 years ago to today, and you might say the average American was developmentally disabled in 1900. That wasn’t the case…
Q: What do you see looking ahead when it comes to new genetic technology?
A: I think the ability to sequence DNA is going to affect how we think about heredity a lot. We are at the point where millions of people are getting their DNA sequenced. A generation ago, that was unimaginable.
It’s going to advance further. People are going to get their whole genome sequenced. It may influence who they decide to have children with. If you realize you and someone else might have a serious disorder, you might rethink it. On the other hand, you might rescreen for variants and avoid them.
And there’s gene editing. We have the ability to edit DNA very precisely. It’s already starting to change the way we breed crops and it could become part of in vitro fertilization. Maybe doctors will edit out a mutation that would cause Huntington’s disease or early onset Alzheimer’s. We have to decide as a society whether we’re comfortable with that.
Q: What are you working on now?
A: I don’t have any huge projects right now. I’ve been focusing a lot on my New York Times column. I’ve been enjoying reporting on advances in DNA sequencing, especially from ancient bones.
When I was starting out in science journalism, no one thought it was possible. There were science fiction novels written about it. Now there are weeks when I have to pick out which ancient DNA to write about!
Q: Anything else we should know about the book?
A: I would like to stress that this is not just a book about genetics. Heredity is more than genetics. Genetics is the science of how we inherit genes and how they influence us. But heredity potentially can do more. I encourage people to think more broadly about what it means to inherit something from their ancestors.
Some scientists argue that human culture is a form of heredity. There could be bacteria that live in our bodies and we might inherit some of these from our ancestors. There may other kinds of molecular forms of inheritance waiting to be discovered. I think we’re going to see in the years to come an extended theory of heredity taking shape, and it’s going to be very exciting.
--Interview with Deborah Kalb