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Last week, a study appeared in PLoS ONE, the peer-reviewed journal published by the Public Library of Science, that drew attention in Israel but made barely a ripple here: That men who’d survived the Holocaust lived longer — significantly longer — than their peers who’d never been under Nazi oppression.

What made the study especially intriguing was its large scale and conscientious design: The authors looked at over 55,000 Polish immigrants, roughly three quarters of whom came to Israel between 1945 and 1950 (directly after the Holocaust, in other words), and about one quarter of whom had come to Israel before 1939. And what did the researchers find? That men who’d experienced the Holocaust between the ages of 10 and 15 lived, on average, ten months longer than their brethren who were already in Israel, and that those who were between the ages of 16 and 20 lived an extra eighteen months.

No one, needless to say, was expecting this outcome. Studies of Holocaust survivors have repeatedly shown that their mental health remained — and remains, in the instances of those who are still alive — more fragile throughout their lives: They reported more anxiety, more depression, and more all-around symptoms of PTSD than the general population. State-of-the-art genetic research also suggests that early trauma can severely damage our telomeres, the protective tips of our chromosomes that defend us against cancer and premature aging. (This is a subplot, coincidentally, on season two of the Israeli television series Hatufim, on which the American Homeland is based.)

And so the obvious question arises: Why has one of the most traumatized populations in the world led longer lives?

The authors offer two theories. The first is the phenomenon of “post-traumatic growth.” It’s an intriguing idea, first developed by a pair of psychologists at the University of North Carolina, which stipulates that many survivors of horrific events emerge with a renewed sense of purpose and meaning, a reorientation toward life. Some of the earliest studies of this phenomenon looked at POWs from Vietnam, many of whom have shown remarkable resilience and productivity (like John McCain), and it’s since been documented in scores of other contexts — in survivors of terrorism and natural disasters, in those who’ve lived through mortal illnesses and the deaths of loved ones.

“We certainly see it here a lot,” says Asher Aladjem, the chief psychiatrist at the NYU Bellevue program for survivors of torture. He mentions one of his patients, who lost a child in the conflict in the Ivory Coast. “He believes God guided him here to make a better life for the rest of his family and himself.”

It is one thing, however, to posit that trauma gives some people a renewed appreciation for life; it is something else entirely to declare that it adds years to one. Whether there’s a correlation between happiness and life expectancy is in fact very much open to debate. Anyone who’s had a life-long cage match with melancholy winces when a new study appears that claims to show a link between depression and a reduced life span (like this one from last summer in the British Medical Journal), and rejoices when a new study comes out that contradicts it (such as this study from February, showing that pessimism was correlated with living longer). This is hardly a settled issue.

“It’s all speculative,” says Avi Sagi-Schwartz, a professor of psychology at the University of Haifa in Israel and one of the Holocaust study’s co-authors. “I have trouble, too, litigating these conflicting data.” But as someone who’s interviewed Holocaust survivors and not simply amassed data about them, Sagi-Schwartz, currently a fellow at the United States Holocaust Memorial Museum, also has a different perspective. “Forget, for a moment, these dry statistics,” he says. “Many survivors will tell you: We won the war. It’s our victory. We have children, grandchildren, great-grandchildren, successful ones.” He says it would be hard to measure how emboldening that is. “Maybe the survivors,” he says, “developed a strong desire to celebrate their victory.”

Perhaps. There’s another possibility, too, however. It’s possible that those who were strong enough to survive the concentration camps (or many years in hiding—it’s impossible to know how the study’s subjects spent the war years) were bound to live longer. And the authors do float this idea:

An alternative interpretation would be differential mortality, meaning that those vulnerable to life-threatening conditions had an increased risk to die during the Holocaust. Holocaust survivors by definition survived severe trauma, and this may be related to their specific genetic, temperamental, physical, or psychological make-up that enabled them to survive during the Holocaust and predisposed them to reach a relatively old age.

This is a much more difficult hypothesis to raise, especially in Israel, where there’s an understandable national dread of saying anything that looks like it blames the victims of the Holocaust for their terrible fate. Sagi-Schwartz says that when he first gave his results to the University of Haifa’s media relations people, they told him, with startling candor, that they found the theory too delicate to include in their press release (and it’s why, Sagi-Schwartz suspects, there’s no mention of this possible explanation in the Jerusalem Post’s story from last week). But it can’t be discounted. As two of his co-authors, Marinus van IJzendoorn and Marian J. Bakermans-Kranenburg (both from Leiden University in the Netherlands), point out in an e-mail, selective mortality could help explain why female Holocaust survivors in their sample lived no longer than those women who didn’t: Their physical strength wasn’t valued as much within the concentration camps.

Yet all these theories, ultimately, are speculative. “I don’t think that selection accounts for it totally,” says Sagi-Schwartz. “Because then you’re saying that the extermination wasn’t random, and that those who were shot in the camps were weaker, and those who were in the gas chambers were weaker.” And we know that’s not true. The Nazis killed the strong and the weak. “So then the question is what, beyond selective mortality, could be another explanation,” he says. “And it could just be the case that survivors developed extra mechanisms of resilience. Maybe they developed the desire to stay alive once it was over — to whatever mysterious extent it’s ever under our control.”