A few years ago, my husband was contacted by genealogists tracking descendants of rabbis from the Lithuanian shtetl of Kelm. The impoverished little town was known for its fierce schools of Talmudic learning, or yeshivas; it was a centre of Mussar – a strict system of ethics based on logic and the rigorous practice of mindfulness, a meditative approach to self-reflection and prayer.

The massive genealogy we ultimately received by email spanned five continents, 16 generations and almost 400 years of grief. My husband’s forebears, rabbinical ancestors of the Kelm elite, were prominent in 1648 when Cossacks stormed the town of Nemirov, then in Russian Poland, now in Ukraine. Some 6,000 Jews had sought refuge behind the fortified walls. But Cossacks carrying Polish flags tricked their way in, reportedly killing children, boiling victims in vats, and flaying them alive. Jehiel Michael ben Eliezer, the rabbi of Nemirov and my husband’s great(x9)-grandfather, ran to the cemetery hoping at least to be buried – but he was clubbed to death, then left to rot. The Martyr of Nemirov is his historic name.

After the slaughter, the rabbis fled to other shtetls across the Pale of Settlement – the swath of Europe covering parts of Poland, Lithuania, Russia and Ukraine where Jews were allowed to live. In 1768, Jehiel’s great-grandson Rabbi Zvi Hirsch of Lysyanka in Ukraine was killed by Cossacks, who chased him from his home near Kiev through Romania and Bulgaria to the Turkish border, hundreds of miles away. Four years later, my husband’s great-great-great-grandfather Eliezer Gutman was born in Lithuania, in the city of Plunge. By 1810, he’d moved to the hardscrabble shtetl of Kelm, becoming the town’s chief rabbi and establishing a yeshiva that became renowned. He died in 1831, aged 58.

Like other Jews forced to flee the Ukrainian pogroms, the Gutmans of 19th-century Kelm were poorer than ever. And under the Second Partition of the Polish-Lithuanian Commonwealth, they were subject to an onerous draft that took conscripted Jewish boys from age 12 and as young as eight; military service was for 25 years. My husband’s great-great-grandmother, Eliezer’s daughter Rebecca, was called ‘the Golden Belly’ in the genealogy because she bore four daughters and five sons who all became rabbis. Like so many other Jews of their generation, most of her offspring booked passage for New York City.

One of those daughters gave rise to a criminal gang so notorious that they were on the front page of the New York City papers for a solid year in 1902. They scammed poor Italian immigrants into buying fake jewellery, and when victims couldn’t pay up, they threw them in a fake jail the family rented from corrupt city officials, controlled by fake cops paid by the family. This line of descendants lived in relative luxury in an elevator building on Grand Street, on New York’s Lower East Side; all their weddings were performed by my husband’s great-grandfather (youngest son of ‘the Golden Belly’), the Manhattan rabbi Judah Sacks. Another of the daughters helped to bring to Jerusalem what would become the massive Mir Yeshiva, founded in 1814 in Belarus; today, it is one of the world’s largest centres for the study of the Talmud, fuelled by Mussar, the ethical system honed by the rabbis of Kelm.

Cousins who stayed behind in Kelm were slaughtered when Nazis gathered them into the courtyard of their great yeshiva and shot them on 29 July 1941; they are buried in a mass grave on a local farm. But most fanned out, landing at the forefront of medicine, law, cosmology, the arts – worldwide. Accomplished, yes. Brilliant, yes. But even when advancements of medicine expanded the lifespans of others, many from the red-haired Kelm clan didn’t live long. The genealogy tracked it all. Rabbi Judah Sacks died in New York City in 1903, aged 58. My husband’s uncle Meyer, a Los Angeles rag-trade impresario, dropped dead after a massive cerebral haemorrhage in 1975, aged 58. My husband’s mother, a torch-song singer, had longstanding heart failure; a great-granddaughter of the Golden Belly, she dropped dead from salty food on a Caribbean cruise in 1997. The most influential leader of Mir in modern times, a cousin to my husband, was such a rock star that his funeral, at age 68, drew thousands of black-coated mourners weeping and pounding the streets of Jerusalem in 2011.

The more I read the genealogy, the more the family seemed doomed. While my relatives were living longer as years went by, many into their hundreds, the Kelm descendants often died relatively young. Worried by the deaths, I urged my husband to see a cardiologist, and the first year he was fine. But the next time he went, aged 60, he had a 95 per cent blockage of his carotid artery, and was weeks away from death. Surgery and medication saved him, protect him still, but I suspect an underlying force: dying young might be the price the rabbis paid for so much hard life, so much burden over so many centuries of grief and terror and pain – a price still exacted by their descendants down the line.

The notion that we inherit the legacy of our ancestors, not just their wealth and facial features, but their good luck and hard knocks, is hardly new. The idea that we carry a family curse and shoulder the burdens of the past has been part of our human mythology for as long as we’ve been able to think. The great devastations of the Bronze Age, when civilisations collapsed; the endless ethnic cleansings across continents and centuries; the earthquakes and volcanoes and tsunamis and floods; the great plagues and pandemics – all get wrapped into the drumbeat of ritual and story we try to pass down. But only in recent decades have psychologists trained in the scientific method begun analysing the impact of history’s traumas on subsequent generations. Only this century have we begun to tally the true, transgenerational toll of these historic debacles, and considered a way to heal.

The most famously studied are the children of Europe’s Holocaust survivors, who suffer higher risk of anxiety, depression and post-traumatic stress disorder than their generational peers. But they are hardly alone. Studies have ranged across the African-American descendants of slaves; the Japanese descendants of Hiroshima and Nagasaki; descendants of the genocide in Rwanda; those whose parents survived the collapse of the Twin Towers in New York City on 11 September 2001.

One of the leading experts in transgenerational trauma is Maria Yellow Horse Brave Heart, a clinical social work researcher at the University of New Mexico, and member of the Lakota tribe. Her 2000 paper on carrying historical trauma is now considered a cornerstone of the field. After Sitting Bull, a leader of the Lakota resistance, was killed in cold blood in 1890 at the Standing Rock Reservation in South Dakota, hundreds of his followers fled in fear to nearby Wounded Knee, where they were massacred, their bodies thrown into a mass grave. ‘This massacre has reverberated through the hearts and minds of Lakota survivors and their descendants,’ Brave Heart writes. And the trauma went on, with Native American children dispatched to boarding schools, sometimes more than 1,000 miles away from families and tribal communities. In these facilities, children were beaten, shackled and chained to bedposts. Conditions were so overcrowded that, between 1936 and 1941, a tuberculosis epidemic killed more than a third of the Lakota population over one year of age.

Brave Heart defines historical trauma of the sort experienced by Native Americans as ‘cumulative emotional and psychological wounding over the lifespan and across generations, emanating from massive group trauma’. The intergenerational response to this kind of trauma includes depression, self-destructive behaviour, psychic numbing, anger and elevated mortality rates from suicide and cardiovascular diseases. Lakota mortality rates for heart disease are, to this day, almost twice the rate for the general United States population; suicide rates are more than double the national average.

According to Brave Heart, these blows from history result in ‘unresolved grief’ and ‘impaired or delayed mourning that is part of the experience of massive loss’. More than a century after the Wounded Knee massacre, Sitting Bull’s descendants are still feeling the pain. As one of them told Brave Heart and colleagues:

I think losing the land was the most traumatic … I remember my aunts and uncles and my dad talked about … how they were treated, some were shot, they were telling me about that my grandmother was shot … They were starved … You know, the big lie, that the people were forced to believe in history books, stand and salute the flag that wiped out a generation, forced into slavery, forced into their church system … There’s a big hole in my heart … where does it stop?

Survivors of history can’t just get over it. They are trapped by the centrifugal force of centuries

The concept framed by Brave Heart has since been applied to historic suffering writ large. Joy DeGruy, a professor of social work at Portland State University, has spent years developing the concept for her groundbreaking book Post Traumatic Slave Syndrome (2005). American chattel slavery, she explains, was 339 years of systematic abuse, of being sold, and beaten and raped. ‘[So it’s not] plausible that people escaped trauma. They just never got treated for it. It just never got acknowledged.’ And because the trauma was never dealt with, the culture continues to propagate it unconsciously. For instance, within the black community, dark skin might be frowned upon. And black mothers might denigrate the accomplishments of their children – a holdover, according to DeGruy, from the days when slavers would be forced to sell smart or attractive slave children to the highest bidder, so best to make them seem less. ‘There’s poison in the cookies,’ explains DeGruy, because maintaining culture requires ‘adaptation and survival’, and all of that is ‘folded in to what it means to live in this skin’ today.

Survivors of history must fight for their recovery in this hard-hearted world. Whenever the topic of slavery comes up, there’s ‘immediate pushback’, said DeGruy. ‘You’re free now aren’t you? I wasn’t there, okay, I didn’t own slaves … Get over it.’ But survivors of history can’t just get over it. They are trapped by the centrifugal force of centuries, and their arcs are still spiralling out.

History’s worst hits have spawned a radical idea: a great flood here, a famine or massacre there, could alter not just our psyches and behaviours but the deep biology of our cells. For those caught in history’s churn, the result can be psychiatric symptoms and chronic disease caused by stress. Because these cellular changes are said to be made not at the level of the genetic code, but ‘above’ the genome – through the molecules that control gene expression – they are called ‘epigenetic’.

Epigenetic trauma was found in children exposed in utero during the Dutch famine of 1944 to 1945, when Nazis stopped food from reaching populations in the Netherlands. As adults, the Hongerwinter babies exposed to stress in the womb turned out overweight with impaired glucose levels and increased cardiovascular risk, compared with unexposed siblings. The cause? A lack of ‘methyl groups’ at a number of key genes. These molecules act like ‘off’ switches by attaching to the DNA helix and stifling gene transcription. For the Hongerwinter babies, this hypomethylation led to the overproduction of certain proteins that affect growth and metabolism, triggering a cascade of cellular interactions that trended toward disease. While these epigenetic effects are uneven, the mode of transmission was surprisingly direct – stress from the mother impacted the gene expression of the developing foetus, greatly increasing the offspring’s disease risk.

Those findings apply to a single generation, yet they tug at the edges of evolutionary theory, in which species change slowly over millennia, not rapidly over the months or years of a single life. Charles Darwin’s process of natural selection holds that nature chooses the best-adapted organisms to reproduce and survive in any given ecosystem. The process operates when DNA sequences mutate randomly, and organisms with the specific sequences best-adapted to the environment multiply and prevail – causing gene expression to shift. Yet as surely as the slow march of Darwinian evolution shapes life on Earth over aeons, scientists have found that epigenetic signals can work each day, and not just through methyl groups. Experience in the environment could also alter chromatin, the molecular matrix making up our chromosomes; RNA, the messenger molecules that translate genetic instructions from DNA into protein; and histones, the proteins involved in packaging and structuring the chromatin comprising the genes.

Male descendants had tumours, kidney disease, prostate disease and immune disease in very high frequencies

Some of the most important work in the field comes from the neuroendocrinologist and stress expert Bruce McEwen at Rockefeller University in New York, who has been studying epigenetic change caused by poverty, addiction and family violence. With his colleagues, he has found that such social stressors increase production of the adrenal stress hormone cortisol. That, in turn, retunes the genes in a brain structure called the hippocampus, degrading synapses between cells and compromising memory and mood. Stress also gets to the amygdala, the brain centre for fear, tweaking genes that expand the structure’s dendrites; the expanded amygdala generates a heightened sense of anxiety when more stress is afoot. Researchers from Duke University in North Carolina studied 132 impoverished adolescents, and found that the chronic stress of noise and violence increased methylation of a particular bit of DNA – the proximal-promoter region of the serotonin-transporter gene (SLC6A4) – indicating a heightened fight-or-flight response within their amygdala and a lower level of serotonin, associated with depression.

Epigenetic changes can occur during an individual’s lifetime or be induced by pregnant mothers when their stress hormones reach the womb. But can they be passed down the generations?

Yes, says Michael Skinner, an evolutionary biologist at Washington State University. He and colleagues report that ‘environmentally induced epigenetic transgenerational inheritance has now been observed in plants, insects, fish, birds, rodents, pigs and humans’. In rodents, such changes can last at least 10 generations and, in plants, hundreds.

In an extraordinary and disturbing series of experiments conducted over the course of years, Skinner has shown just how devastating epigenetic damage can be. To do his work, he exposed mice to a series of one-time environmental toxins, including the insect-repellent DEET, the plastic BPA (bisphenol A), the historic insecticide DDT, and hydrocarbons such as jet fuel and oil, during a key period of foetal development, when sex organs were forming in the womb. By the second generation and every generation thereafter without further exposure, he reports, male descendants had tumours, kidney disease, prostate disease, testicular disease and immune disease in very high frequencies. Four generations out, the effects seemed truly transgenerational: female descendants suffered ovarian failure, polycystic ovarian disease and premature puberty. The overwhelming majority of offspring were easily stressed, and many were obese. ‘Ninety per cent of the animals have multiple diseases,’ Skinner says. Without any further exposure, each toxin precipitated a unique biological fingerprint in the form of an altered epigenome, and a unique disease profile passed from one generation to the next.

Could this kind of phenomenon explain the Kelm rabbis’ early sudden deaths due to cardiovascular disease? Research in cardiology now traces atherosclerosis, vascular disease, arrhythmia, artery disease and even cardiac hypertrophy to epigenetic effects – in the individual. Testing whether we can extend such findings across generations will take more time. While exposure to maternal stress can alter a baby’s epigenome, the per cent of culture and biology that carries trauma forward, for humans is still unknown.

Whatever we find, it hardly takes a pogrom for stress to paralyse families and reverberate down the line: poverty will do just fine. McEwen and colleagues have amply demonstrated the adversity in those who grow up in ‘risky families’ that are merely unsupportive, neglectful and cold. The worse the abuse, the more profound the epigenetic effect on the hippocampus, the amygdala and even the centre of cognition – the frontal lobes. From this perspective, many adult diseases are actually developmental disorders that begin early in life with poverty, discrimination or maltreatment, and could have been reduced by the alleviation of toxic stress in childhood, McEwen explains.

Whether epigenetic changes last just the lifetime of the individual who lived through the trauma or are passed down like genes, ‘We can never roll back the clock and reverse the effects of experience,’ McEwen says. ‘We can move through those experiences to recovery and redirection; also, we can develop resilience through epigenetic change. New trajectories can engender compensatory changes in the brain and body over the life course.’

We can also reverse epigenetic effects on the brain. According to McEwen, the hippocampus increases in size with regular exercise, with intense learning, with antidepressant treatment. One study showed that walking an hour a day improved cerebral blood flow and memory in the elderly. Mindfulness-based stress-reduction decreases the size and activity of the amygdala – which, since it is the centre of fear, is all for the good. Even an antidepressant such as Prozac can open the windows of brain plasticity – as long as cognitive therapy is used to rewire as well.

In one of the most ambitious reviews of the data on resilience to date, researchers from King’s College London found a wide range in the way that individuals react to extreme adversity and stress. ‘While some individuals develop psychiatric conditions such as post-traumatic stress disorder or major depressive disorder, others recover from stressful experiences without displaying significant symptoms of psychological ill-health, demonstrating stress-resilience,’ they wrote. Among the factors that helped people to overcome toxic stress by working around the epigenetic damage it leaves, the researchers suggest social connectivity, a sense of humour, and a proactive approach to life’s many hard knocks.

Native Americans were never allowed to truly grieve, and their ‘historical unresolved grief’ has made things worse

Brave Heart discusses the importance of going through traditional forms of grief. For the Lakota, that means the concept of ‘Wakiksuyapi’ – maintenance of a connection with the spirit world and identification with ancestors from their historical past. Native Americans were never allowed to truly grieve, Brave Heart says, and their ‘historical unresolved grief’ has made things worse.

Beyond all this, medical science seeks to target epigenetic damage caused by environment or stress with potent drugs. The target is the damage done to an individual within that person’s lifetime – but could be expanded more widely if transgenerational epigenetic inheritance turns out to be important in the human realm.

This could be the best news of all, because the idea that we might cure disease through the big Human Genome Project of the early 2000s has failed to bear fruit. In fact, most genetic variants identified so far confer relatively small increments in risk, and explain only a small proportion of disease clusters in families. A growing number of researchers now hope that the epigenome will fill in the missing heritability gap. Bradley Bernstein, an expert in cancer epigenetics at Harvard Medical School in Massachusetts, says that some glioblastoma brain tumours and leukaemias, in particular, emerge from epigenetic changes in the form of ‘hypermethylation’ in cells, and can be fought with drugs that reverse the methylation process.

The cancer epigeneticist C David Allis at Rockefeller University has been working on epigenetic treatments for cancer – and his therapies based on the histone proteins that DNA coils around have already been effective for some patients considered untreatable in the past. Increased production of RNA, another epigenetic pathway, has been associated with acute myocardial infarction, coronary artery disease and heart failure, and these could be targets for therapies of the sort that might aid descendants of Kelm. Researchers are seeking epigenetic treatments for diabetes, schizophrenia, obesity, ageing and inflammation as well. A significant, robust body of evidence shows that epigenetic mechanisms can explain a lot of the asthma we see in the modern world.

Aside from treatments to cure the already-afflicted, understanding the phenomenon means preventing epigenetic damage before it occurs – protecting our young people from poverty, toxic stress, pollution, abuse and garden-variety neglect. It means social policies and cultures that boost resilience while lowering risk. Brains must be protected by government regulations and business environments that promote adequate healthcare, affordable education, strong families, flexible working hours and ample vacations. According to McEwen:

Healthy behaviours and humanistic policies can ‘open a window’ of plasticity and allow the wisdom of the body to exert itself. With the windows open, targeted behavioural interventions … can shape brain circuits in a more positive direction. Even if one has gotten off to a bad start in life, the trajectory can be changed.

What about me? The genealogists who tracked the Kelm rabbis also helped me unravel my origin, a long-held secret on my father’s side. My grandparents never told any of us about the brutal place they came from, and even the family name, Weintraub, turned out to be a kind of ruse. I was tipped off to the mystery back in 1979, when my cousin Robert told me an old man had stopped him on the street in Be’er Sheva, Israel, insisting he’d met our grandfather on the boat over to Ellis Island in New York City around 1901. ‘Your face is the same, exactly,’ he told Robert, ‘but the name, it wasn’t Weintraub.’

My cousin, a pragmatic chemist, told the baffling story like a joke. ‘Ridiculous,’ he said. But our oldest aunt confirmed. ‘The name started with “A” maybe,’ she guessed – but her memory was dim. A search through ship manifests and records in recent years revealed that the New York Weintraubs once ran stores on the main drag in the Ukrainian shtetl Shpikov, the armpit of the universe, where bathrooms were outhouses in everyone’s front yard and Cossacks still roamed through to rough up the Jews. Back then, the name had been Aizenman, or some facsimile thereof – and those Aizenmans, records show, had come to Shpikov not long before leaving it, from a lace-making town to the east. Adding spice to the story, an elderly cousin told me that every generation, one of the blue-eyed ‘Weintraubs’ was born dark, like her – expressing genes from very far east, she claimed. ‘My mother called me ugly. We dark ones were pariahs,’ she said.

On my mom’s side, meanwhile, the family name was Nichamoff – and a cousin hypothesised our relation to a certain Russian admiral, Pavel Nakhimov, for whom ships and a naval academy had been named. That imperial admiral’s history includes a Jewish wife and children: perhaps explaining why my maternal grandfather always looked ‘Swedish’ to me, with his blue eyes, golden hair and upturned nose.

Have I divested my own life baggage only to carry the pain and sorrow of my ancestors?

To trace my own transgenerational trauma through history’s great commotion, I gene-test with my brother – but there’s no big reveal. We share 50 per cent of our genes, great gobs of blue all over the chromosome map on Family Tree DNA. I find other so-called relations on the genealogical listings, but if we share any trauma of history, it appears to be the trauma of the world. Ten generations back, I have – gulp – 1,022 ancestors; 12 generations back – 4,096. Yes, at the modest rate of four generations a century, more than 4,000 people have combined to make me in just 300 years – my ancestry is diffuse and vast. I’m not even totally Jewish, to my surprise. I’m also eastern European of non-Jewish origin, supporting the admiral story. Also Italian. Also West Asian. Also East Asian – supporting the strain of ‘dark’ my elderly cousin described. I look around at direct relatives, those I have known in the real world – my mother, aged 98. My aunt Fannie, who lived to 105, and Rose to 104. My dad, to 94. Unlike the fragile rabbis, my resilient family lives long. ‘We’re going to be in this forever,’ I tell my brother. As for those I find in the genealogical lists, I share with them only small, diffuse snippets of DNA. It’s hard for me to say what trauma I’ve picked up from history through any given timeline and from where. I am no descendent of the red-haired Kelm clan – my genes have been through too many cycles and rinses and worlds.

Besides, there’s something creepy about the thought of ancestral tags in my DNA, even if it’s true. I come from New York City, from the kind of intellectual Jewish family where, during the 1970s, the extended network of cousins on my mother’s side thought that, to be evolved, one had to go through psychoanalysis. The therapist I saw had a giant, splashy Andy Warhol lithograph of Martin Buber on the wall. And after years of reviewing my life, Buber’s was the lesson I took away: ‘I and thou.’ After excising the ‘thou-ness’ of my family from my mind, I learned to stop projecting their image on the world. Or so I thought. Now, after all that work, I don’t relish the news that the pain and sorrow of my ancestors might be etched in my cells. Have I divested my own life baggage only to carry theirs?

I’ll put such worries aside. The study of epigenetic effects across generations is still at the starting gate, and findings in rodents don’t directly translate to us. In a skeptical look at the field, published in 2016 in PLOS Genetics, a trio of researchers including John Greally, director of the Center for Epigenomics at the Albert Einstein College of Medicine in the Bronx, argue that, on an individual basis, studies could be subject to false positives, publication bias and sloppy data, overall. The data sets are small, and sometimes the markers found could have pre-dated the diseases they are said to signal. The work awaits large funding, replication and widespread scrutiny and review.

Instead of mourning my past, I’d rather stay tuned to the evolutionary moment in the world at large. We are all in this together, after all: my brother’s two sons, who studied in Indonesia, now have Indonesian wives. ‘I’ll be having brown grandchildren,’ my brother cheerfully says. Many of my cousins – or their children – now have married outside the faith. Even the Kelm rabbis have thrown in their lot with the universe through their thousands of descendants, who go by names such as Wolpert and Finkel and Gutman and Sacks. Motion, dilution, remixing – they are givens of our diverse and modern world. The goal for most of us should be looking forward, to shepherd what comes next. When do conditions become so extreme, so polluted, so stressful or dangerous that we risk damaging the epigenomes of the unborn? When does an event or situation rise to the level of epigenetic emergency? When do we risk humanity, and what must we do to set the balance right?