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In his 1859 book “On the Origin of Species,” Charles Darwin envisioned evolution like a branching tree.

The most suggestive evidence for such transgenerational transmission may come from a macabre human experiment. In September, 1944, amid the most vengeful phase of the Second World War, German troops occupying the Netherlands banned the export of food and coal to its northern parts. Acute famine followed, called the Hongerwinter—the hunger winter. Tens of thousands of men, women, and children died of malnourishment; millions suffered it and survived. Not surprisingly, the children who endured the Hongerwinter experienced chronic health issues. In the nineteen-eighties, however, a curious pattern emerged: when the children born to women who were pregnant during the famine grew up, they had higher rates of morbidity as well—including obesity, diabetes, and mental illness. (Malnourishment in utero can cause the body to sequester higher amounts of fat in order to protect itself from caloric loss.) Methylation alterations were also seen in regions of their DNA associated with growth and development. But the oddest result didn’t emerge for another generation. A decade ago, when the grandchildren of men and women exposed to the famine were studied, they, too, were reported to have had higher rates of illness. (These findings have been challenged, and research into this cohort continues.) “Genes cannot change in an entire population in just two generations,” Allis said. “But some memory of metabolic stress could have become heritable.”