Carl Zimmer is a rarity among professional science writers in being influential among the scientists on whose work he writes and comments – to the extent that he has been appointed as professor adjunct in the department of molecular biophysics and biochemistry at Yale University. Zimmer has just published his 13th book, She Has Her Mother’s Laugh, a survey of “the power, perversions and potential of heredity”.
What is the book’s main message about our attitudes to heredity?
Heredity is central to our existence and how we define ourselves. But it’s not what we think it is. It’s not just genes, for example. We inherit culture too, and there may even be other channels of heredity. And the way genes enable heredity doesn’t fit our common notions. We tend to imagine that we inherit particular genes from our parents, grandparents and so on, and that these shape us in ways that are easy to understand and trace. But that’s not how heredity works. Each trait is typically influenced by hundreds or thousands of different genes, and the environment in which those genes are acting makes all the difference to how we turn out.
You talk in the book about how some of these questions were brought home to you when your first daughter was born in 2001. What’s your personal journey into the story of heredity?
In 2000 my wife was pregnant with our first child, and our doctor asked us to go to a genetics counsellor. I thought this was pointless. But the counsellor started asking me questions and I suddenly realised I had a really terrible grasp of my family history. I felt very ashamed and irresponsible, because here was this child who would be inheriting a lot of my genes. This was the first time heredity went from being something I learned about in class to one of the most important things in my existence.
Linking our traits to genes still has bad connotations for some people. Why is that?
In the 19th century, people like Charles Darwin and Francis Galton framed heredity for the first time as a scientific question, and by the early 20th century some thought they had found the complete answer in genetics. In the short term, that had a terrible social impact, because several scientists and politicians felt we knew enough to control heredity for the betterment of society: to practise eugenics.
These incendiary questions haven’t gone away. The links between genes and intelligence or race are still hotly debated. What is your take on those connections?
There are lots of different ways to define intelligence, but the tests do measure a factor that is stable across people’s lifetimes and that is partly heritable. That’s a firm result, both from studies of twins and now looking directly at genes.
Yet environment certainly affects outcomes too. Take height. It’s much more heritable than intelligence, but each gene on average just makes people an eighth of an inch taller or less, and there are over 3,000 common genetic variants that influence height. On the other hand, everyone across the world today is a few inches taller than they were a few hundred years ago, and that has nothing to do with genetics. It has to do with better food, better medicine, better health systems.
A hundred years ago, people would use the discovery of genes to dismiss all the problems that face society, like poverty. They’d say: this is just genetic, and the only thing we can do to make it better is start sterilising people.
One of the main ways our picture has changed in recent years is the concept of epigenetics: how genes are switched on and off in different cells at different points of our development and life. How important is that?
Effects from the environment can turn on and off genes in a long-term fashion, and epigenetics is what makes that happen. So what your epigenetic profile looks like when you’re 50 depends on your life – the various contingencies and strokes of good and bad luck that you’ve had.
There have been some studies suggesting that epigenetic effects can be inherited – but this is controversial. Do you believe it?
The possibility of epigenetic inheritance is intoxicating because it raises the possibility that experiences can produce biological changes that are then passed down to future generations. It has completely taken popular culture by storm. We now have epigenetic skincare, epigenetic yoga… I’ve seen a book by a psychotherapist claiming that you can heal your psyche by treating the traumas of your grandparents that have been passed down to you.
But there’s a lot of scepticism in the scientific community about the evidence for it in humans. The experiments are tantalising, but the studies are small, the effects are small, they haven’t been replicated, and they really strain the imagination because you have to rethink a lot of basic biology just to make the idea work.
The story of heredity may be changed by the fact that we can now edit genomes. Should we?
We shouldn’t try to look to our genes for some quick, simple way to make life better. There are a few cases where that is going to be the case, but many more where it’s not. For example, Huntington’s disease or sickle-cell anaemia are life-threatening diseases encoded by a single gene mutation. You can imagine treating someone born with sickle-cell anaemia by rewriting a little bit of DNA in their cells to give them a supply of blood cells that don’t have this mutation, and in theory they should recover and lead long and healthy lives. It’s hard to argue with that.
But when you intervene in a tiny clump of embryonic cells in a way that will pass down altered DNA to future generations, you need to think about what could be the broader effects. The risk could come when people read about the genetics of intelligence and say: “How much do I have to pay to get that programmed into my child?” It’s going to be hard to have any real control over this stuff. If one country says we’re only going to allow genome editing for fatal hereditary diseases and nothing else, then people may just go to some clinic in another country where they promise the moon and the stars for your children. In fact, this is already happening.
You have had your own genome sequenced. What did you find out?
The prospect of looking at my own genome was thrilling and terrifying at the same time. It turned out I didn’t find anything to get particularly worried about. But I did learn a lot about my DNA. I’ve discovered exactly which pieces of DNA I inherited from Neanderthals and how they may influence my health. I’ve learned that I’m missing vast chunks of DNA found in other people. And I’ve also learned how hard it is to draw lessons from your own unique sequence of DNA.
Are people being allowed to do this testing without a full grasp of the real implications this information might carry?
It is a kind of wild west. Companies, to a greater or lesser extent, will provide warnings about the information you might get and how to deal with it. For example, some people find out that their immediate family is not what they thought it was – maybe the person you thought was your father isn’t. These are the things the tests can reveal in a pretty clear-cut way, and they can be devastating.
Where things get a little more problematic is when people try to read some sort of profound significance into the results about their ancestry. Say someone finds they are part Italian when they thought they were just German and Irish. It doesn’t make a lot of sense to start breaking out the pasta that you never liked before – as if your DNA carries culture on it. That’s just not how these things work.
The more we understand about how heredity actually works and about our own values about heredity, the better experience we have of these things.