Corporal Calvin Bates, of the 20th Maine Infantry Regiment of the Union Army, was taken prisoner by Confederate soldiers in May 1864, during the American Civil War (1861-1865). He was only four months in the prison camp of Andersonville (Georgia) but left there emaciated, sick, with both feet amputated and intense suffering in his eyes (see photo). So tough were the conditions that 40% of the prisoners did not leave alive from there. Now, a study with thousands of them shows that the children that the survivors of that hell had lived less than those of other veterans. They even died younger than their brothers born before the war. Somehow, the pain of their parents was recorded in their genetics.
For years, animal studies have shown that certain environmental factors cause changes in genetic information that pass from one generation to another. It is as if they left marks that turned off or ignited genes but without altering the DNA. This has proven that the sugar that parents take can make their descendants obese or that the bad nutrition of the grandparents would harm the health of your future grandchildren. Despite the great impact it could have on science and health, little is known about these epigenetic mechanisms in humans and knowing more would require experiments that ethics prevent.
That is why the history of Bates and the social experiment that involved the internment of some 200,000 Union soldiers in southern prisons during the war that divided the United States is so exceptional. A group of researchers from the University of California in Los Angeles (USA) have tracked what happened to them once they left the fields. Thanks to the military archives, they know if they were married or already married, where they lived, what they were engaged in or when and how many had children. They could also see when they died, their wife and children. They verified that, as they publish in PNAS, those who had after going through places like Andersonville lived less than the children of other war veterans.
At the same age, the children of prisoners conceived after the war were twice as likely to die
"Two things happened in the field: starvation, with the men turned into walking corpses that died of scurvy and diarrhea, and psychological stress," says UCLA economist and lead author of the Dora Costa study. Neither she nor her colleagues are genetic specialists or have been able to study the DNA of the 6,500 war veterans and their 20,000 children who have investigated. But they have reached the epigenetics by discarding: Controlling various factors, such as socioeconomic status, origin, date of enlistment, previous health status … compared the longevity of the children of veterans who were prisoners of those who did not, seeing that, in the same circumstances and at the same age, the former were twice as likely to have died. There is another data that reinforces the thesis of the epigenetic base: Within the same family, the children that the prisoner of war had after surviving one of those fields were up to 2.2 times more likely to die before their brothers to the same age.
"Certainly there is intergenerational transfer of traits in humans, something that can happen by well-known methods, such as Genetic heritage or cultural heritage, such as learning, "recalls Neil Youngson, professor at the University of New South Wales (Australia)." What is special here is that this research shows a different inheritance mechanism, epigenetics, in the that an environmental exposure (in this case hunger or stress, the authors can not say which) induce molecular changes in the gametes that, in turn, affect the health or behavior of their descendants, "explains this researcher, not related with the study.
Until now, the few social experiments that have allowed us to study the intergenerational transmission of trauma in humans had had as protagonists children, even still to be born, but not adults. In the last months of World War II, the north of the Netherlands, still under German domination, suffered a terrible famine. In cities such as Rotterdam or Amsterdam rations did not reach even 1,000 kilocalories a day. Hunger affected the fertility of women, but the worst would come later: the children of pregnant women in those months were born with an average of 300 grams less. As adults, that prenatal exposure to hunger reduced their body size and increased the incidence of diabetes and schizophrenia.
These effects are sometimes manifested in the third generation. In 2017, a work with a huge sample of 800,000 Swedish children proved that the trauma of losing a father or mother leaves a mark that children inherit. Their authors saw that children who remain orphaned in the years before adolescence tend to have, as adults, more premature and lighter children than those who did not lose their parents. "Just before puberty, during the period of slow growth, it is when spermatogenesis is scheduled and when the testicles begin to form, it is also a psychologically formative moment and in our study we saw that a serious psychological trauma, the death of a father , during this period predicted the results at the birth of children of children, "explains the researcher at the University of Stockholm (Sweden) and co-author of this study, Kristiina Rajaleid.
The daughters of the prisoners of war, however, were as long-lived as the children of the other veterans
One of the fathers of the epigenetic hypothesis of trauma transmission is the researcher at the Karolinska Institute (Sweden), Lars Olov Bygren. Together with the British geneticist Marcus Pembrey, Bygren carried out the call Överkalix studio in which they observed a relation between the availability of food at an early age and the health status of the descendants among the inhabitants of a small town above the Arctic Circle. In particular, they found that the grandchildren of those who, as children, had suffered hardships due to bad harvests, have higher incidence of cardiovascular problems. "We have seen three periods sensitive to the transgenerational response, the first months, up to two years, during the period of slow growth [en torno a los 10 años] and in the 17-18 years, "says Bygren in an email Many of those who enlisted to fight the Confederates were that age.
But there is one last piece of information from the study of prisoners of war that intrigues scientists: the trauma of so much suffering was only inherited by the sons, the daughters were as long-lived as the rest of those who went to war. Neither the authors nor the experts consulted know with certainty the reason for this discrimination by sex. Equally the analysis of the data of the third generation, of the grandchildren and granddaughters of soldiers like Corporal Bates, which is in progress, can explain it.