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Image: Oxford University Press

How do we become who we are? Traditionally, people’s answers have placed them in one of two camps: nature or nurture. The one says genes determine an individual while the other claims the environment is the linchpin for development. Since the 16th century, when the terms “nature” and “nurture” first came into use, many people have spent ample time debating which is more important, but these discussions have more often led to ideological cul-de-sacs rather than pinnacles of insight.

New research into epigenetics—the science of how the environment influences genetic expression—is changing the conversation. As psychologist David S. Moore explains in his newest book, The Developing Genome, this burgeoning field reveals that what counts is not what genes you have so much as what your genes are doing. And what your genes are doing is influenced by the ever-changing environment they’re in. Factors like stress, nutrition, and exposure to toxins all play a role in how genes are expressed—essentially which genes are turned on or off. Unlike the static conception of nature or nurture, epigenetic research demonstrates how genes and environments continuously interact to produce characteristics throughout a lifetime.

We spoke with Moore to find out more about the science of epigenetics, its impact on the nature versus nurture debate, and the hopes and cautions that come with such a potentially revolutionary line of research.

Evan Nesterak: How does the science of epigenetics change the seemingly age-old nature versus nurture debate?

David Moore: For the longest time, the nature-nurture debate has been cast as a kind of contest between genes and experiences. The thought was that we might have some characteristics that are caused primarily by genetic factors and other characteristics that are caused primarily by experiential factors. What epigenetics is making clear is that’s a faulty way to think about the situation, because it’s not true that genes do things independently of their contexts. Instead, genes do what they do because of the contexts that they’re in. Nature and nurture are always working together to produce all of our traits.

EN: Can you describe a study that you feel illustrates the science of epigenetics?

DM: The one that has drawn the most attention has been the one done by a team of researchers led by Michael Meaney and Moshe Szyf at McGill University. These researchers watched how rat mothers interacted with their babies. They discovered that some mothers naturally lick and groom their baby rats more than other mothers do. They also noticed that the mothers that licked and groomed their rats the most wound up with offspring that grew up to be adults that were less stressed out when they were put into mildly stressful situations. The mothers that licked and groomed their baby rats less wound up with offspring that were more stressed out. In order to determine if this was an effect of experience, the researchers cross fostered the baby rats, so the ones born to the high licking and grooming mothers were raised by the low licking and grooming mothers. What they found was that it was the perinatal experience that made all the difference. It didn’t matter who you were born to—if you were raised by a low licking and grooming mother, you would grow up to be a more stressed out adult rat.

So the question was, how can it be that these kinds of early experiences can have these long-term effects later on in adulthood? Meaney and Szyf traced the effect to epigenetics. Specifically, they discovered that in certain brain cells of baby rats, there are certain genes that get turned on when the babies are licked and groomed. Then, the turning on of those genes leads cells to build proteins that help moderate stress responses into adulthood, because the genes stay turned on. Meaney and Szyf’s work shows how it is that an experience can influence what an animal’s genes are doing, in a way that can have a long-term effect.

EN: Can you describe how epigenetic research relates to humans?

DM: We don’t know as much about this, because we really can’t do tightly controlled experiments with human beings for ethical reasons. As a result, we don’t have a particularly concrete understanding about how this all works in people. But the reason I wrote my new book, The Developing Genome, is because we have enough circumstantial evidence to suggest that things are happening in humans much as they’re happening in Meaney and Szyf’s rat pups.

There are really two ways in which we can get insight into what’s going on in people. One is by looking at experiments that have been done on our primate relatives, the monkeys. There are a variety of studies on monkeys that show effects like those discovered in rats, where experiences influence the epigenetic states of certain genes in certain cells in monkeys’ bodies. The second way we can get insight into epigenetic phenomena in people is by doing correlational studies. In this way, even though we’re not doing experiments, we can see if certain kinds of experiences early in life are correlated with later epigenetic states in actual people. So far, these kinds of studies have revealed that this is indeed the case.

It’s not true that genes do things independently of their contexts…genes do what they do because of the contexts that they’re in.

Scientists have also discovered epigenetic effects of experiences that are less related to psychology. For instance, when they’ve looked at certain cells in the muscles, they’ve seen epigenetic effects of exercise. And when they’ve looked at other cells in the body, they’ve seen epigenetic effects of diet.

EN: Can you describe from an epigenetics perspective what is known about how an experience like poverty might impact an individual’s biological processes and their outcome?

DM: Yes and no. Again, I need to start off with a caveat. There is very little that we know for sure at this point, because it’s not like scientists can do experimental studies in which they randomly assign people to grow up in poverty, so it’s hard to know for sure what’s going on. Having said that, there is an increasing amount of data that suggests that growing up poor has long-term effects on people. Let’s say we’re studying a person who grew up in an impoverished environment, but as he got older, the person was successful and reached a higher socioeconomic status. If scientists compare such a person’s epigenome to the epigenome of someone born into the higher socioeconomic status, and who has managed to stay at this level, they’ll find that the person who was poor in childhood has a different epigenetic state than the person who was born into greater wealth, even if both people are now equally wealthy. So, poverty seems to have consequences that produce effects that can be detected in the body decades later.

EN: In your book, you describe the pitfalls of genetic determinism and you caution against people creating an epigenetic determinism. For instance, because a person was born into poverty they will be X or because they’ve had this experience they will be Y. Can you describe the potential hazards of this type of thinking?

DM: I don’t think people know enough about epigenetics yet to be epigenetic determinists, but I foresee that as a problem. As soon as people start hearing about these kinds of data that suggest that your early experiences can have long-term effects, there’s a natural assumption we all make that those experiences are determinative. That is, we tend to assume that if you have this experience in poverty, you are going to be permanently scarred by it.

The data seem to suggest that it may work that way, but it also seems to be the case that the experiences we have later in life also have epigenetic effects. And there’s every reason to think that those later experiences can ameliorate some of the effects that happened early on. So, I don’t think we need to be overly concerned that the things that happen to us early in life necessarily fate us to certain kinds of outcomes.

EN: How does epigenetics make us rethink the idea of genetic inheritance?

DM: To me, there’s been a surprising amount of hype related to epigenetic inheritance. That’s because there is some evidence that the experiences we have in the course of our lives can change our epigenetic states and those epigenetic states can then be transmitted to the next generation. This has caused a bit of an uproar among some biologists. They are unsure about what to do with this new finding, because it calls to mind a pre-Darwinian biologist named Lamarck who argued that evolution occurs when the experiences we have change our bodies and we pass those bodily changes on to our offspring.

Asking which is more important, genes or environments, is kind of like asking which is more important in making an ordinary automobile run, spark plugs or gasoline. You need both. They’re both absolutely essential. Asking the question “which one is more important?” really doesn’t make any sense.

Lamarck’s idea was abandoned in the 19th century after Darwin’s theory rose to the fore. The truth is, Darwin was actually a Lamarckist and he wasn’t opposed to this idea, but a lot of the neo-Darwinians—the people who picked up Darwin’s theory in the early 20th century and ran with it—they were very opposed to Lamarck’s idea. The presence now of some data that suggest that our experiences can produce biological effects that can then be transmitted to the next generation has alarmed biologists who were trained to believe that Lamarckian inheritance is impossible.

I think it’s now clear that this kind of transgenerational transmission is possible, although it might be rare. We still don’t know for sure yet. One thing to keep in mind when thinking about epigenetic inheritance is that it’s potentially scary, because imagine if you’re exposed to a pesticide, for example, or some other environmental toxin. If that exposure has some sort of epigenetic effect on you, the prospect that your great-great grandchildren might be influenced by your experience is somewhat worrisome. But these kinds of swords typically cut both ways, so there’s also the possibility that people can have experiences that might somehow improve the lives of their descendants. This is all still poorly understood, but it makes it an exciting time to be doing research in this area.

EN: Given the revolutionary nature of some of these findings, how has your thinking changed as a result of the rise of epigenetics?

DM: I became interested in these kinds of questions long before epigenetics became popular. When I was a naïve graduate student, one of my hopes was that I might be able to tease apart nature and nurture by working with babies. But it became clear to me very early in my career that it was not going to be possible to do that, because by the time they’re born, babies have already had 9 months of experiences inside of their mothers, and many of those experiences are influential. Thinking seriously about development made it clear to me that nature and nurture can never be teased apart, because influential experiences are an important part of natural, normal development, starting immediately after conception.

EN: How are other scientists reacting to epigenetic research? Are people optimistic? Is there a rift?

DM: I think everybody is optimistic and excited. I think everybody knows that there are a lot of really interesting and important things to be learned from doing this kind of work. Of course, there are also differences in perspective.

Whether you talk to biologists or psychologists, if you ask them outright, they will almost invariably tell you that genes and environments always interact to produce our characteristics. But my experience has been that if you press them a little bit, you will find that their interactionism is actually rather shallow. For instance, it can often be revealing to ask someone about a characteristic like Phenylketonuria—widely considered to be a genetic disease—or about a characteristic like eye color. When you ask most people if characteristics like these are more influenced by genetic factors than by environmental factors, they will typically say “yes.” So even though everybody says “I understand that genes and environments interact,” they are still under the mistaken impression that one of these kinds of factors can be more important than the other. But that’s just not right. Given how genes and environments interact, each kind of factor is always just as important as the other in influencing the final form of a trait.

We are on the threshold of a whole new way of thinking about human development.

There’s an analogy I like to use to illustrate this point. Asking which is more important, genes or environments, is kind of like asking which is more important in making an ordinary automobile run, spark plugs or gasoline. You need both. They’re both absolutely essential, and it’s the same for genes and environments. Asking the question “which one is more important?” really doesn’t make any sense. Yet in spite of the fact that most people will tell you that genes and environments interact, they’ll also tell you that some characteristics are more genetic than others, even though this can’t be right. Research on epigenetics has really driven this point home. So, I think as we learn more about epigenetics, there will need to be some change in theoretical perspective among some scientists.

EN: Is there anything else you would like to add?

DM: I have seen a number of books coming out about epigenetics that contain a lot of unsubstantiated claims. It’s [been] picked up by some writers who use it to suggest that simply by changing our attitudes, we can potentially use epigenetics to heal ourselves in certain ways. And while it’s possible that that’s true, there really isn’t any good data to that effect yet, so we just don’t know.

The bottom line is that we are still very much in the early stages of understanding this aspect of molecular biology, and it’s a bit too early for anyone to either sound alarm bells or to argue that we’ve discovered a magic bullet that’s ultimately going to solve our health problems. There’s a lot more work that still needs to be done before we understand all of this, but it certainly looks like we are on the threshold of a whole new way of thinking about human development, and it’s very exciting.

David S. Moore

David S. Moore is a Professor of Psychology at Pitzer College and Claremont Graduate University in Southern California. He received his Ph.D. in developmental and biological psychology from Harvard University. A developmental cognitive neuroscientist with expertise in infant cognition, his theoretical writings have explored the contributions of genetic, environmental, and epigenetic factors to human development, and his book The Dependent Gene was widely adopted for use in undergraduate education and was nominated for the Cognitive Development Society’s Best Authored Volume award.

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