In a landmark 1997 paper in , he showed that natural variations in the amount of licking and grooming received during infancy had a direct effect on how stress hormones, including corticosterone, were expressed in adulthood.The more licking as babies, the lower the stress hormones as grown-ups. Two alcoholic mice — a mother and her son — sit on two bar stools, lapping gin from two thimbles.

Likewise, Michael Meaney, a Mc Gill neurobiologist, had been talked into attending by the same colleague, who thought Meaney’s research into animal models of maternal neglect might benefit from Szyf’s perspective.“I can still visualize the place — it was a corner bar that specialized in pizza,” Meaney says. Since the 1970s, researchers had known that the tightly wound spools of DNA inside each cell’s nucleus require something extra to tell them exactly which genes to transcribe, whether for a heart cell, a liver cell or a brain cell.

“Moshe, being kosher, was interested in kosher calories. One such extra element is the methyl group, a common structural component of organic molecules.

Sometimes methyl groups attached to DNA thanks to changes in diet; other times, exposure to certain chemicals appeared to be the cause.

Szyf showed that correcting epigenetic changes with drugs could cure certain cancers in animals.

Without any change to DNA at all, methyl groups could be added or subtracted, and the changes were inherited much like a mutation in a gene.

Now, at the bar in Madrid, Szyf and Meaney considered a hypothesis as improbable as it was profound: If diet and chemicals can cause epigenetic changes, could certain experiences — child neglect, drug abuse or other severe stresses — also set off epigenetic changes to the DNA inside the neurons of a person’s brain?Geneticists were especially surprised to find that epigenetic change could be passed down from parent to child, one generation after the next.A study from Randy Jirtle of Duke University showed that when female mice are fed a diet rich in methyl groups, the fur pigment of subsequent offspring is permanently altered.Originally these epigenetic changes were believed to occur only during fetal development.But pioneering studies showed that molecular bric-a-brac could be added to DNA in adulthood, setting off a cascade of cellular changes resulting in cancer.A January storm has deposited half a foot of snow outside the picture windows lining his fourth-floor corner office at the Douglas Institute, a mental health affiliate of Mc Gill.