GUILFORD, Connecticut — Born to an Ashkenazi Jewish father and mother of Irish and German descent, science and heredity has long fascinated Carl Zimmer.
But when his wife became pregnant with their first child, heredity became a matter of urgency. He wondered what his child would inherit from him and how that inheritance would get passed down to future generations. Being a dedicated science journalist, Zimmer embarked on a quest to decipher the meaning of heredity.
To properly tell the story he knew he needed to delve into one person’s genome. And whose better than his own?
After he had it sequenced, he showed the results to several researchers and had them interpret the findings. He discovered he carries genes for two serious diseases and that he has many identical genes with a typical Nigerian and Chinese person. But perhaps most importantly, Zimmer learned heredity isn’t what we think it is.
Just what defines heredity is addressed in his new, 675-page book “She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity.” In it he explains why some children resemble their parents and others don’t, why humans are bent on putting people into racial categories even when race doesn’t exist, and why DNA and lineage are not one and the same.
As Zimmer writes, heredity exists beyond genes — it exists in the “microbes that swarm our bodies, to the technology we use to make life more comfortable for ourselves.”
The following interview has been edited for brevity and clarity.
You decided to post your genome online for scientists and students to analyze. What were your privacy concerns, if any?
I had given the data to several scientists. They showed me how they go through a genome and try to learn something about it. Then they said it would be a shame to throw away all this analysis. They suggested setting up a website where my whole genome and their analysis is posted as a resource for people.
I thought about it a lot and talked to a lot of people. There’s a big debate among ethicists and among scientists about whether this [making individual’s genomes public] is a good idea. Some people think it’s a terrible idea and some people think it’s an incredibly good idea. There are some scientists who say the only way to discover new things about why we get sick is to be able to look at as many genomes as possible.
It was a pretty easy decision for me to make because my genome is relatively boring. Let me put it this way. I consider myself much more than my genome. I could tell you my birthday, the color of my hair and my zip code and that would tell you much more about me.
You wrote extensively about the ethical issues of gene editing such as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats). Are there areas of gene research that should stay off-limits?
I’m leery of people saying we absolutely should not study our genome. That doesn’t make sense to me. You can jump to conclusions that aren’t warranted or you can be careful. I don’t have any problem with people studying any part of human nature so long as they’re not using it to justify existing prejudices.
I write a lot about how we inherit height and how that can be really important for understanding a whole bunch of diseases, including cancer. On the other hand, if someone says we should allow parents to change whatever genes they want with the promise their children will be tall and successful, that would be incredibly irresponsible.
No one says we should do this research so we can sterilize people. They say pinpointing these genes might tell us something new about how the brain works
Some people will say studying genes and intelligence is a bad thing. They will point to the horrible history of people making claims about intelligence to justify sterilizing people or executing people or banning people from immigrating to a particular country. I’ve reported a lot in this field and talked to many scientists. No one says we should do this research so we can sterilize people. They say pinpointing these genes might tell us something new about how the brain works.
As you wrote, ancient DNA doesn’t simply debunk the notion of white purity, it debunks the very name “white.” Still it seems we humans are light years away from internalizing the scientific fact that race is a social construct.
I’m actually optimistic that people are learning our shared history. The more you dig into your genetic inheritance, the more you realize any simple ideas you had about putting people into groups falls apart.
That said, race is incredibly important in the United States in terms of social groups. If you do a study on what is the median wealth of a white family and what is the median wealth of a black family, the disparity is incredible. It really speaks to the legacy of slavery, Jim Crow laws, and being shut out of GI benefits. So if you use the term race you need to be aware these disparities don’t exist because black people have one gene and white people have another. That’s simply a fallacy.
So much of how we define family and kinship was turned on its head in the chapter ‘Individual Z.’ I finished that chapter thinking we are related to everyone and we’re related to no one.
It’s easy to assume ancestry and genes are the same thing. That’s just not true. If you have an ancestor and they passed down a copy of a gene to a child and you repeat that over many generations, you might end up with a descendant inheriting no DNA from that ancestor.
We have some desires about genealogy that genealogy just won’t give us. For example, we want to find someone famous in our ancestry. Maybe it’s boasting, maybe it’s just excitement because we think of it as being rare and special. It’s not. It just isn’t. Everybody in Europe is probably descended from Charlemagne — everybody. There’s actually a special society in Europe for descendants of Charlemagne and I want to tell them they need to open their membership to about a billion people.
In the book you talk about cultural heredity — the idea that we teach each other and pass down culture from one generation to another — for example, how to farm, how to construct buildings. Do we also inherit intangible traits such as fear or stress?
I think any sorts of beliefs or behaviors that aren’t hardwired into us are passed down through cultural heredity. People’s fear of spiders and snakes is literally in our genes. You can see apes and monkeys also have the same instant fear response to snakes. Nobody has to teach you to be afraid of these things.
Likewise, nobody has to teach you to learn a language, though what language you learn is not in your genes. The language you learn is part of your cultural inheritance.
Regarding ancestry/DNA tests, you talk about how there aren’t enough rare variants to really pinpoint where any of us — including Ashkenazi Jews — come from.
The Ashkenazi community hasn’t existed for time immemorial. It emerged in the Middle Ages in Europe and became distinctive because it was very small. There was one study that suggests the founding population of Ashkenazis might only have been 350 people. While the population grew over the next centuries, the people tended to marry among themselves. They usually weren’t going to marry the Christian next door. This is a classic way for a group of people to become genetically identifiable.
It’s the same thing for people living on an isolated Pacific island or in a rainforest with little outside contact. If you keep bringing in the same genetic variants into the next generation among a limited selection of people it’s just going to become more and more recognizable.
Did you find similar results with Sephardic and Mizrahi Jews?
The research isn’t there the same way. That’s partly because the United States pioneered a lot of this research and scientists who wanted to look at a population of Jews in the United States were going to look at Ashkenazi Jews. That’s how the BRCA1 gene was discovered.
I personally didn’t look at into Sephardic populations because I wanted to use my own heredity as a guinea pig to understand my past.
Aside from a handful of cases where children sued their parents for allowing them to be born with congenital diseases — so called “wrongful birth” lawsuits — do you anticipate other cases along these lines?
I can imagine in the future some kids might sue their parents because they didn’t use CRISPR to make their DNA better. I would hope that case would be thrown out of court.
It’s getting easier to know the genetics of unborn children. Right now there are some research labs that can take a blood sample from a pregnant woman, pluck out the cells from her fetus and sequence the entire genome of that unborn child. If that child goes on to develop some painful disease that was totally encoded in their genes, they might ask why their parents didn’t do something when they could.
Do you think you look at people differently now?
I actually catch myself trying to guess people’s ancestry just based on their appearance alone. I recognize what a presumptuous thing that is to do because our ancestry is so complex. Within any population people’s looks vary enormously. How we define ourselves ethnically has a lot more to do with society than it does with biology.
A few years ago 23andMe came out with an interesting study. They asked people to identify their ethnicity. Some answered white, some black, some Hispanic and so on. They compared people who identified as black with how much African ancestry they had. People with less than 20 percent tended to call themselves white. However, if it was more than 28% they tended to call themselves black. That’s an arbitrary number, which says a lot about our country’s past: the one drop rule; the advantages that came from passing in the 19th century so you could have legal protections.
I actually catch myself trying to guess people’s ancestry just based on their appearance alone. I recognize what a presumptuous thing that is to do because our ancestry is so complex
So I try to bear all that complexity in mind when I’m with other people and recognize my radar can’t be very good.
What’s one thing that makes you excited about the future of genetic research?
As part of my research I ended up hanging out for a while in Pennsylvania, in Amish country. Amish people descend from a small population of Swiss farmers who came to the US in the 1700s and stayed close to themselves. The population tends to suffer from a bunch of devastating hereditary metabolic diseases that are almost unheard of in the rest of the world.
A local clinic figured out how to rapidly test these babies within hours of birth. If they get diagnosed with these diseases they are immediately put on special diets. This saves lives. I met some of the kids who benefited from this and they’re just happy teenagers.
What is one thing that makes you wary about what you’ve discovered?
I’m worried people will still try to tell themselves simple stories about heredity and that they’ll use those stories to justify doing bad things. That is my worry. If we gain more power over our biology those problems can become more dramatic.
What’s your advice for people who are considering genetic testing like AncestryDNA or 23andMe?
It’s not going to tell you how you’re going to die.
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