The James J. Peters Veterans Affairs Medical Center in the Bronx is one of those out-of-the-way places where America warehouses the casualties of its wars. It’s a functional place, surrounded by a high fence, that looks like a cross between an urban community college and a low-security prison. Inside is a modern no-frills hospital that smells like a mix of heavy-duty disinfectant and vegetable soup. While it is not uncommon to see men of all ages in combat jackets or fatigues, no one is wearing a complete uniform. The handful of women I see in the hallways appear to be widows. No one who is doing exceptionally well in life shows up for treatment at a VA hospital in the Bronx. It is a closed universe, inhabited by people who have been permanently altered by the physical and psychological wounds of combat, perhaps the most painful of which is that they are treated like lepers by a society that is made deeply uneasy by their sacrifice.

Rachel Yehuda, the director of the Mental Health Patient Care Clinic at the Peters Medical Center, and a professor of psychiatry and neuroscience at the Icahn School of Medicine at Mount Sinai Hospital, is one of the world’s leading experts in post-traumatic stress. In addition to tending to injured minds, Yehuda has used her brilliant mind and the intuitions drawn from decades of clinical work to become one of the pioneers of the emerging field of epigenetics, which seeks to identify the mechanisms by which traumatic stress may permanently alter the physiology of survivors in ways that are passed on to their descendants.

That epigenetics may have particular relevance for the self-understanding of the Jewish community is an idea that is hardly lost on Yehuda, whose parents are Israeli and who spent a decade working with Holocaust survivors and their children. In the hope of understanding her field better, I met Yehuda in her small, government-furnished office in the Bronx, where she spends most of her working hours. She is a lively, empathetic woman with a lightening-fast mind, whose ego seems grounded in the knowledge that she is using her enormous emotional and intellectual capacities to help others. When I mention that it is snowing heavily outside, she glances over at the window to make me feel comfortable, and then realizes that the shade is drawn.

What is epigenetics?

Epigenetics refers to the study of alterations on genes that change the way the genes function. An epigenetic mark is literally a change to the gene or to the DNA environment that will then affect the way the DNA is read into RNA, and subsequently how RNA is expressed into a protein.

Are you saying that the experiences of human populations—famines, wars, other experiences like that—are encoded into our genes? That we take our history with us?

I think you’re saying that. You just asked me to tell you what epigenetics was. You didn’t ask me about how you get an epigenetic change.

How do you get an epigenetic change?

Well, an epigenetic change occurs from the environment. So there’s something in the external environment that affects the internal environment, and before you know it a gene is functioning in a different way. Epigenetics has been something that cancer researchers studied for a long time because it helped explain how a dramatic change could occur in the environment of a person to cause a tumor. But it’s become interesting now in neuroscience and mental health because it helps answer questions that have not been answered either by classic genetics or by stress theory. And those questions involve, “How do you create an enduring transformative change that isn’t genetically programmed?”

When it comes to trauma exposure, what people will say is that they’re changed. You hear veterans saying, “I’m not the same person I was before the war. I left myself on the battlefield.” A rape victim might say the same thing. People don’t talk in terms of fight or flight language, which is: There’s a stressor, a reaction, the body calms down, and homeostasis and recovery are achieved.

I was violently raped, or I was blown apart on a battlefield, but guess what? I’m totally fine now! I’m back!

Almost nobody says that after trauma. If they are resilient, and they don’t feel broken anymore, they can acknowledge that. But it’s still not “back.” “Forward,” maybe. Or, “different in a positive way.” Or, “I’ve somehow taken this adversity and transformed myself into a better version of myself,” which some people call “post-traumatic growth.” But almost nobody says, “I’m back.” Because trauma changes people permanently and in an enduring way. And so the language of epigenetics, the science of epigenetics, offers a very tangible way for understanding how environmental events can permanently change things. And it also offers a mechanism for potentially understanding how those changes can be transmitted to the next generation.

The idea that those permanent changes are encoded in us in a way that can be passed on to our children and affects their physiology is a startling idea. Can you explain in a little more detail the mechanism by which that happens? Our DNA literally becomes different, or it’s read differently? How does that work?

Our DNA becomes different and is read differently. But the question is whether this is transmitted through meiosis or through, I guess, sex cells, or whether it is acquired based on a parental response to their environment. And there are epigenetic mechanisms that can be linked to both of those things.

Another type of a change can be based on changes in the in-utero environment that can become incorporated into the offspring based on what is happening to a mother during her pregnancy. And yet another mechanism involves completely post-natal changes. You didn’t inherit the DNA change, but there was something so different about the way the parent is responding to having a new baby that the behavior between mother and child, or parent and child, is altered as a function of parental trauma.

The first demonstration of this was by a scientist named Michael Meaney in McGill, and he did studies in rodents, where he removed the mother for a few minutes, and put the mother back in the cage. And the mother would begin to behave differently toward the rat pups. And he could see by having—simply on the basis of differences in the licking and grooming behavior of the mother, he could induce a change in the rat pup that was permanent and dictated the way that rat offspring would respond to stress forever, and through the different generations. He began by looking at one region in one gene in the hippocampus. And that was the glucocorticoid receptor gene, the gene that is responsible for the activity of the cortisol receptor. Then the work obviously expanded to other genes, other regions.

What we decided to do was look at that same gene in blood in connection with Holocaust offspring. That’s how our work began. We found changes in the same gene. There are also other studies that have to do with responses to famine in the second and third generation.

Can you talk a little bit about the famine studies?

One of the first observations was that in women who had been exposed to starvation, they tended to have babies that were born with altered enzyme activity and were at subsequent risk for hypertension and metabolic syndrome, simply as a consequence of maternal starvation during the pregnancy. Now, the enzyme that was altered is also an enzyme that is related to glucocorticoid function. It’s a very interesting enzyme. It’s an enzyme that converts active cortisol to inactive cortisol. And cortisol is a glucocorticoid. So, we were very interested in that because we wondered how much of our effects in offspring in general had to do with maternal starvation. And we did a study where we looked at Holocaust survivors, and we found that within the Holocaust survivors themselves, there were alterations in this enzyme. So, we then looked at the children of Holocaust survivors and found alterations in the enzyme in the opposite direction in the children, but particularly this was based on the maternal age during the Holocaust. So, mothers who were younger during the Holocaust transmitted a different enzyme change to their offspring, compared to mothers who were adults during the Holocaust.

What this suggests is that there’s some kind of different change that may be occurring as a result of the age of exposure, or pre-puberty or development that then gets transmitted differently in the case of that system. We know that the age of exposure is important. We know that the environment in which someone is pregnant is extremely important. We know that by studying women who were in the World Trade Center on 9/11 and were pregnant, and following them for several months, and their offspring.

What were the effects you observed in the children of World Trade Center survivors?

Women who were in the second or third trimester gave birth to babies that had low cortisol if that mother had PTSD. And if the mothers had PTSD, but they were in their first trimester, we didn’t see the low cortisol effect. So, from this we learned that there must be some kind of an in-utero influence that interacts with the biology of PTSD, and a different result occurs. We also learned that mothers who were pregnant and in the World Trade Center towers on 9/11 gave birth to babies that were smaller for their gestational age. So, there are all sorts of effects in utero that can have big effects on offspring. So, we now have a language, we now have a methodology, and we can begin the task of unpacking this.

I know the offhand reaction of someone like my father, for example, or other post-Soviet people is, “Well, wasn’t that Joseph Stalin’s great contribution to science, Lamarckian adaptation?”

In my circles, Lamarckian genetics wasn’t such an accepted thing, even though there is evidence of it everywhere. Lamarck didn’t talk about epigenetics; he observed a phenomenon that was true, but he didn’t have a mechanism to explain why it occurred, the way Mendelian genetics could explain things. Scientists like to know how things happen. Now, with epigenetics there is a real possibility of understanding really more enduring changes and how changes that occur at the molecular level can really have high yield. The question becomes: How enduring are these changes? What other kinds of influences can change them yet again?

Think about the difference between writing something in pencil and writing something in pen. If I write something in pencil, it’s there, but I can erase it pretty easily if I want to, if it gets wet or something like that. The way that I think about this—for right or wrong—is that a person can acquire a new set of tools for an unforeseen circumstance, and then to the extent that their environment is similar, they use the tools, and they need the tools, and they pass the tools on. And to the extent that there is a complete mismatch between the tools that they’ve been given in their environment, maybe they don’t.

So, for example, if a mother was in Auschwitz and was starving and transmitted the biology to the offspring—it’s a biology that allows your liver to hang on to free cortisol and not have it converted to inactive cortisol, so that you can effectively get by with less fuel—that would be a fantastic thing for an offspring to have under periods of starvation. But if the offspring lives in a country where a breakfast bagel can feed a family of two for a day, there is a mismatch between that biology and what has been given.

Epigenetics provides a mechanism for short-term adaptations. And the word “adaptations,” it has positive connotations. Adaptation is good. Gene mutations take generations. We can’t wait for evolution. You gotta act quickly. So, the idea of being able to, at critical periods, transmit something based on unforeseen circumstances is a very good idea. And then the question is: What will your environment be like, and how will you cope with the fact that you have a set of tools from someone traumatized, but you’re not—or don’t need to be?

Except you probably were traumatized by growing up with parents who were changed by their own traumatic experiences.

So, that’s where this field gets a little mushy-squishy, because it’s not strictly about changes on genes anymore. You’re dealing with a very complex set of issues that are based on: what was the child-rearing like; and what were the circumstances like; and what were the overriding factors? All of these things combine together to determine whether or not what you’ve inherited—either genetically or epigenetically—becomes useful to you as a person. If the environment can transform you in one way, it can transform you in another way too. If we make little changes in very important circuits, this can have a very big impact on health and well-being.

There’s a quote in Ezekiel, “The fathers ate sour grapes, and the children’s teeth were set on edge.” So, the Jewish culture and religion has understood that children bear the burden of their parents’ legacy. Fair or unfair, it’s a fact. It’s a cultural fact. It’s a biological fact. Everyone is born with a unique set of genes. The task is to refine from these traits the best self that we can have and not get distracted by the traits that are weaker; build up the traits that are stronger. We all have the same job to do.

A century ago, there was a spate of movements that aimed to produce a new man: the new socialist man, the new communist man, the new Zionist Jew. All of these movements in some way posited that you needed to modify the environment in order to bring out a different set of traits, and then that would in turn produce a new and better kind of human being. Obviously those were crude ideas, but you’re suggesting they weren’t entirely crazy.

It’s not a crazy idea. When you look at the Haredi community, which I understand because a lot of it is familiar but so much more is unfamiliar, that seems to have to do with being in a very enclosed environment, where the environment itself can help solidify the differences and create a new reality for generations and generations and generations to come. Now, is that epigenetics; I don’t know. Somebody in the future may study that and know. But I think the part that epigenetics adds to that concept is that it is actually possible to change your DNA based on your environment. That’s a powerful concept.

The Jews of Europe, at least, were a people who went through repeated selection events of mass trauma, hunger, persecution, and slaughter. So, you would probably be looking at some pretty major epigenetic effects in that population as a whole, a bunch of enzymes and markers that would have been turned on or off.

But to me the Jewish people seem also very diverse. Even if you take the smaller subset of Jews called “children of Holocaust survivors,” or even children of Holocaust survivors from a particular concentration camp or region in Europe, they’re not all the same. Though the event and trauma exposure may be a strong contributor to something, there’s still this other biology that is about individual response that is either a sum total of highly unique events, or is the thing that keeps us from being solely responsive to events. I suppose you can, from a cultural perspective, decide that Jews are more alike than other non-Jews, or you can look within Jewish people and say, “Hey, there’s quite a bit of variance here,” which is what I tend to do. I focus on the variance.

My friend Edward Luttwak compares Israeli society to a soup that his housekeeper makes. He says that the soup has to be left to cook over a low to medium flame all day long, and then it tastes amazing. But if the heat is too low, it tastes terrible. And if you turn the heat up too high, it also tastes terrible. His point being that this particular society functions better with what we would regard as an intolerable level of stress, because that’s what these people are optimized to deal with. If you take that away, they actually become less productive, less creative.

From my perspective, I’m more interested whether or not the low flame is going to have the same effect on the carrots and the peas. That is what I’m interested in. Or whether the low flame will have different effects on two individual carrots. So, the idea of a flame being too high or not being there at all, that’s nice in terms of understanding what it takes to catalyze any biologic change—that’s correct, you have to have something, but not too much. Too much is death. Too little is not enough environment for anything to occur. But the question is where we want to put our focus in terms of understanding how different things work. We can focus on the unit of analysis that’s generalizable to every ingredient, or we can ask, “What are the differences?”

For decades, the field of stress research did the first thing: What is the effect of a stressor? What I’m interested in is how people fundamentally transform themselves, because this is not such an easy thing to do. We are to some extent prisoners of our biology and our environments. We can theoretically choose our environments; in practice, our choices are more limited based on our genetics, and a lot of factors that are superimposed on our presumed free will. But I’m always going to be interested in the differences.

Having grown up in a community that had plenty of Holocaust survivors, I don’t think that there was a single one of those families that hadn’t been given a spin by their trauma. On the other hand, the spins were different. Some of them were exceedingly amoral people. Some of them were exceedingly moral and charitable people. Some of those people were severely disturbed and psychotic people, while some of them were very gentle and kind people. You saw every kind of effect. The only thing I’d say about the effects is that they tended to be relatively extreme compared to the effects of growing up in a normal American suburb, I guess.

That’s the point. In other words, what’s new here is that we’re trying to understand whether the different responses were there before, or whether trauma made them that way. We’re trying to understand whether resilient people are born or made, whether in order to be resilient you actually have to have the trauma exposure, or whether you would have expressed the trait of resilience even in the absence of an environmental change.

The resilience was switched on by the traumatic event.

Yes. And that is very new. In the past, the idea would have been, “Well, that’s the kind of person they were.” Their pre-trauma traits would determine their post-traumatic responses. People who are generous before are generous before are generous after, people who are religious before are religious after. But that’s just like saying that trauma is not that relevant. And I don’t believe that. I think the trauma is highly relevant. But then the question is: If the trauma is highly relevant, how do I produce such different post-traumatic responses?

It’s a very big question. If we respond to traumatic experiences based on who we are before the trauma, then we can have a lot of success in building resilience before anything bad ever happens. Then we should presumably be able to develop a formula and test it biologically. That really gives people an enhanced skill set to be able to respond in a completely optimized way to adversity. If what you’re like before a trauma has a lot less to do with your response to an event, then that’s something that we want to know also.

So, if I ask a very simple question like, “If you’re a child of Holocaust survivors, are you more likely to respond differently to a car accident,” that’s very concrete. We did this study, and we published it, and the answer is: Yup, you’re three times more likely to respond to a traumatic circumstance by getting Post Traumatic Stress Disorder if your parent had Post Traumatic Stress Disorder. So, then you have a place to begin to wonder, “Why is that so?” Is it because the Post Traumatic Stress disorder in the parent is there because of a gene that was there before the trauma? Is it there because of an interaction with the gene and the environment? Is it completely a de novo response to an environmental stressor? Does it have something to do with what happened after the trauma? Is it some interaction of all of this? And in the offspring, are you carrying the gene? Are you carrying an epigenetic change? Are you carrying the legacy of a behavioral response in the parent that then makes you more at risk? If you’re 4 years old and your mother freezes when she sees a policeman, and you notice it cause you’re holding her hand and she’s not safe—to most people a policeman is a safety signal, but not to your mother—what is the impact of that on you?

Culture is the ever-evolving product of an ever-evolving group of people. So, if you have a large number of people whose parents or grandparents have been traumatized, and you can show that the effects—whether transmitted by maternal behavior, by epigenetic effects—then, in turn, the weight of having a very large number of people having very different kinds of responses to a policeman or whatever, are going to shape the literature, and art, and codes of behavior within that group, and provide a vehicle for the transmission of trauma responses to people who did not have parents who physically went through those particular events. So, culture can also be the bearer of trauma.

I think that’s an excellent point. I think you’re also explaining why someone like me, whose parents are Israeli and have really very little connection to the Holocaust, feels that the Holocaust was my trauma too. But I think it’s very important to make sure that people understand that not all effects of trauma are negative. What you have represented among children of Holocaust survivors is a preponderance of people that are in therapeutic professions: doctors, nurses, social workers, psychologists. You have an extraordinarily large number of people that go into tikkun olam, fixing what’s broken. I think that that’s also a response to a cultural trauma. You can get stuck in the legacy of victimization, or you can say, “No, no, no, no, no. I’m going to be part of the solution.” I don’t know why in the Jewish culture, you have an overwhelming response of, “I’m going to make sure this doesn’t happen again.”

When I was running the Holocaust offspring clinic in the ’90s during Darfur and all of these other events, I was so struck with the passion of Holocaust offspring to want to go, to do, to make sure the Holocaust never happens again. They have heightened radar for genocide. To me, it really felt like a post-traumatic response, but in a positive way. But it equally could have been, “What can we do? They’re always going to kill us. They’re always going to kill everybody.” There could have also been a highly disempowered response. Maybe because, as they would say, they’re children of the survivors.

But that’s always been a debate: Is it really survivorship, or luck, or both? But it’s all of the above. I think that that’s what’s interesting from a cultural perspective; that from a cultural perspective, there’s very little in the way of victimhood. Nobody points to the Jewish nation and says, “What a bunch of victims,” because that isn’t really what happened. So, whatever the epigenetic change is, whatever damage was done, whatever difficulties there may have been in connection, or relations, or attachments, you know, the things that Holocaust offspring sometimes talked about in therapy – from a cultural perspective, the second and third generation are not apathetic people, but highly intelligent people who have used the experience in some measure to make the world a better place, heal the sick, make sure it doesn’t happen. Whether that’s in the DNA or not, I don’t know, but I think it’s certainly the culture overall.

Another thing I’ve noticed about Jews is that have a special affinity for marijuana rather than alcohol. They really like it. Why?

Endocannabinoids. The gene that converts alcohol to acid-aldehyde, and basically affects your tolerance for alcohol, is very culturally over-determined. Many Asians and Jews have similar intolerance to alcohol based on this gene, and other cultures over-indulge because, again, a variance in this gene. I don’t know if that’s epigenetic or genetic, but there’s probably something to the fact that we are attracted to these substances if we have an experience with them based on differences that we bring in. We have receptors for opiates. They’re already in our bodies. We have receptors for marijuana, nicotine, alcohol. So, our body is set up to respond, and the individual responses may be genetic. So, I think that that’s part of the discussion. I like to think of genetics as the computer, and the epigenetics as the software, the app, the program.

I was recently pitching a TV show to some Hollywood people, and I found myself telling a story about Jews being wired for one thing, and then coming to this country, where suddenly a people that was wired for struggle and starvation and oppression—

Could go to the supermarket.

—suddenly found abundance. Jews created most of modern American mass culture, from the movies, to television, to the fashion business, cosmetics, the music industry, mass-market paperbacks, all these ways of packaging and selling democratic pleasures to the masses. And at the same time, this group of people also went crazy. A cultural—you might say cultural-genetic—set that had been wired for one kind of environment was plunged into an environment that, certainly by the 1950s and 1960s, had become a radically different environment from the one those people were programmed to function in.

Again, I’m always going to focus on the differences, because I think that an understanding of the differences will eventually lead to the knowledge of what is core. I am very fascinated by the circumstance of two people having very similar experiences and coming out quite differently. You can’t change your DNA, that’s for sure. But if you can change the way your DNA functions, that’s sort of the same thing.

I sense that for you the plasticity of our genes is a hopeful thing.

It’s tremendously hopeful. It’s wonderfully encouraging, because it means you have a tremendous amount of power to be the best version of yourself possible.

Do you think it’s fair to speak of Jews, given their history and especially in the wake of the Holocaust, as a traumatized people, whose genoplasm has been altered by a particularly difficult set of experiences?

I don’t think it’s a constructive way to think about anyone. I think it would be more helpful to say it’s a resilient population that has been able to overcome adversity at great cost, perhaps.

And based on your knowledge of that community and your insight into some potential shaping genetic effects of its historical experiences, what would your advice to this community be? Relax more? Be ever on the alert for genocidal maniacs who may afflict you and the rest of humanity?

My message is that there’s a reason that you behave the way you do. You have to ask, “Is my behavior helping me optimize myself and my environment?” If yes, fabulous. Give your mother a kiss, and your father too. You want to change? You were given a set of tools for a certain set of circumstances that maybe, thank God, you don’t have to deal with. If you do, you have the tools. And if you don’t, you might want to think about your own children, and what environment you want to better prepare them for.

So, I think the message is to think about whether you feel comfortable in the world as an individual, as a Jew, as a member of a larger society, and a larger world, and then take an inventory of how well you are living in the world. And then feel empowered, because science has shown us that you can change a lot of what you don’t like, or override a lot of what you can’t change.