Thursday, December 13, 2018

The DNA of Shared Experience

The modern science of genetics has made it clear how parents can pass aspects of their own specific heritage along to their offspring. And, indeed, the reason no one finds it at all startling to assert that specific physical traits can be transmitted from generation to generation is precisely because we can see easily enough how a child’s hair color or eye color often matches one or both of his or her parents. From there, it’s not that much of a leap to considering non-physical attributes—say, a predisposition to excel at athletics or as a musician—in that same vein. And, indeed, we also all know instances of children appearing naturally to be good at some skill at which one of their parents excels (or at which both do). But can that notion be extended to include specific experiences parents may have had as well? At least at first blush that sounds like a stretch: the notion that something can happen to me and that that experience can somehow end up encoded in my DNA if it only crosses some theoretic line of genetic responsivity—that feels hard to imagine. But learning about the science of epigenetics has altered my thinking in that regard, and altered it powerfully. What I’ve learned in that regard is what I want to write about this week. And also about its implications for my understanding of the nature of Jewishness itself.
I was prompted to start taking the possibility of the transmissibility of experience seriously by a study published in the Proceedings of the National Academy of Sciences just this fall. Written by Dora L. Costa, a professor of economics at UCLA, and by Noelle Yetter and Heather DeSommer of the National Bureau of Economic Research in Cambridge, Mass., the study focused on data from Civil War days and concluded that the sons of Union Army soldiers who suffered severe trauma in the course of their time as prisoners-of-war in Confederate prison camps were significantly more likely to die without reaching old age than the sons of Union soldiers who were not captured or incarcerated by Confederate forces. Since all the sons in the study were born after the end of the war, the study suggests that they must have—or at least could have—somehow inherited their fathers’ traumata and suffered from their aftereffects. There were even subtle gradations of experience to consider: the sons of men who were imprisoned in 1863 and 1864, when conditions for prisoners of the Confederacy were especially brutal and inhumane, seem to have been even more likely to die as young people than the sons of Union soldiers taken captive earlier on in the war. (To see the original study, click here. For an excellent analysis of the study published in The Atlantic last October that most readers will find far more accessible, click here.)

The phenomenon has been demonstrated to exist in the animal kingdom as well. A few years ago, for example, scientists were able to demonstrate that when mice who were trained to associate the smell of cherry blossoms with the pain of electric shocks were bred to produce offspring, both the next generation and the generation after that responded anxiously and fearfully to the smell of cherry blossoms in a way wholly unlike mice whose parents or grandparents hadn’t been trained to associate that scent with that level of pain. The study, written by Emory University School of Medicine professors Brian G. Dias and Kerry J. Ressler and published in the journal Nature Neuroscience, concluded that the mice had somehow inherited a response built into their parents’ history of experience. (For a very interesting account of this experiment published in the Washington Post a few years ago, click here.)
And then there came the study of the Dutch famine victims. In the winter of 1944-1945, to punish the Dutch for having attempted to assist the Allied advance into Europe by shutting down the railway links that were being used by the Germans to bring troops to the front line, the Nazis blocked food supplies from coming into Holland so severely that more than 20,000 people died of starvation by the time the war ended the following spring. (For more information, the best source is Henri A. van der Zee’s The Hunger Winter: Occupied Holland 1944-1945, published in 1998 by the University of Nebraska Press.) This would just be one more horrific story of German savagery during the war, but it led to some interesting scientific studies, one of which was published jointly by seven scholars led by Professor L.H. Lumey of Columbia University in the International Journal of Epidemiology in 2007 and which appeared conclusively to prove that the wartime experience of famine impacted not only on the poor souls who had to live through that dreadful winter in the Netherlands, but on the children born to them after the fact: as a group, the children of people who lived through the famine and survived to become parents later on experienced higher rates of obesity, diabetes, and schizophrenia than their co-citizens. They were also noticeably heavier than Dutch people born to parents who did not live through the Hunger Winter. And they died younger than other Dutch people did on the average—the study found that people born to Hunger Winter parents were still experiencing a full 10% higher rate of mortality even sixty-eight years after the famine ended. How exactly this all works, or might work, is beyond me. (Click here for the study itself and here for a far more easily understandable summary of its results published in the New York Times last winter.) But what seems easy to seize is the basic principle that the severe trauma suffered by people living in occupied Holland while the Germans were actively trying to starve the civilian population into submission was so severe that children born to those people ended up with the experience somehow encoded in their own DNA even though they themselves did not experience the famine at all.

This accords well with an essay by Olga Khazan published last summer in The Atlantic in which the author was able very convincingly to demonstrate that victims of intense racial discrimination seem as a class to experience a process called methylation on the specific genes that are connected with bipolar disease, asthma, and schizophrenia, and that this specific genetic change too can be passed along to subsequent generations. What methylation is exactly is also beyond me. The simplest explanation I could find was on the website (click here), but was still far too sophisticated for a mere liberal arts major like myself to fathom. The basic principle, though, is clear enough: the experience of intense discrimination can apparently imprint itself on your DNA in a way that makes it possible for children born to you even long after the fact to have to deal with traumatic experiences they didn’t personally experience because those experiences have somehow ended up encoded in their DNA.
And that brings me to the Jewish angle in all of this.  Just two years ago, Dr. Rachel Yehuda of Mount Sinai Hospital here in New York discovered evidence of this methylation process affecting the gene associated with stress not only in the DNA of Shoah survivors, but in the DNA of their descendants as well.  The study, published in Biological Psychiatry in 2016 and not meant for any but specialist readers, was not universally praised—but mostly because only survivors and their children were included in the study, but not the survivors’ grandchildren or great-grandchildren. (For an example of a hostile response published in the U.K. in 2015, click here.) But those scientists are basing themselves, as scientists surely should, on the specific way Dr. Yehuda used the empirical data that was available to her. I, on the other hand, not being encumbered by an actual background in science, find her work wholly convincing and more than easy to believe. Indeed, I have spent my whole life wondering where Jews like myself, who can reasonably say that not a single day has passed since adolescence in the course of which some thought or image related to the Shoah has not surfaced invited or uninvited in my consciousness, from whence this obsessive involvement in the Holocaust derives. Both my parents were born in this country. Therefore, neither was personally a survivor. But both were adults when the war ended and the details regarding the camps and the mass executions became known; the trauma the Jewish community experienced over the months that it took for the true story to become known—and the compounded trauma of slowly coming to terms with the degree to which the Allied forces chose consciously not to interfere with the daily transfer of Jews to the death camps—that trauma, it now seems to me, is at the core of my own worldview, of my own sense of who I am and what the world is about.

Nor is this just about the Shoah in my mind. recently updated my DNA profile and declared me genetically to be 100% Ashkenazic Jewish. (I had previously been hovering between 96% and 97%). Am I also carrying around the epigenetic markers associated with the First Crusade and the butchery and devastation the Crusaders brought to the defenseless Jews of the Rhineland? I suppose that will only seem an obscure question to readers who don’t know me personally. 

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