In the winter of 1944-45, the Nazi occupation cut food rations in the Netherlands to about 400 calories per day. The Dutch Hunger Winter lasted five months and killed 20,000 people. Pregnant women who lived through it gave birth to smaller-than-average babies — a finding nobody found surprising.

What was surprising came later. Those babies grew up with unusually high rates of obesity, diabetes, and cardiovascular disease. Their children — conceived long after the famine ended, to well-fed parents — also showed elevated risks. Three generations removed from the famine, the effects are measurable in the DNA of Dutch people alive today.

The mechanism is called epigenetics. The DNA sequence itself didn't change — but chemical markers on top of the DNA, tiny methyl groups that switch genes on and off, were rewritten by the experience of starvation. These marks propagate through cell division and, sometimes, through generations. A grandmother's famine can tune her grandchildren's metabolism for starvation that never arrives.

The same pattern shows up elsewhere. Descendants of Holocaust survivors show altered stress-response genes. Great-grandchildren of men who experienced severe famine as boys in 19th-century Sweden have different life expectancies. Grandchildren of mice exposed to a specific odor paired with electric shocks react to that odor instinctively — without ever being exposed.

Your biology isn't just what your parents handed you at conception. It's partly a record of what they, and their parents, and their parents, lived through. The traumas, famines, and abundances of the last few generations are encoded above your DNA, silently tuning you.

Inheritance is stranger than genetics alone suggests.