Epigenetics and Buboes

I've been doing some reading lately on epigenetics, which is the process by which genes are turned off or on based on external stressors, without changing the underlying DNA sequence.  The idea is that most of the DNA in a person's chromosomes is largely unexpressed, but certain sequences can be turned on if, for example, a person is exposed to DDT or dioxin or just general environmental stress.  Epigenetics allows for those newly-activated or newly-suppressed genes to be passed to children.  This process has been proved in mice, and researchers are studying the process in people to show how second and third generations are affected by their ancestors' stress.  In other words, if your grandfather developed diabetes due to environmental factors, the chance you will get diabetes even without experiencing those same factors rises.  The environmental risk for him has become a genetic risk for you.

This got me to thinking about the Black Death, the worldwide plague in the 14th Century that wiped out a third to a half of Europe's population.  Epidemiologists have traced the disease vector to a bacterium carried in fleas in turn carried by rats.  Geneticists have studied the current version of that bacterium to see if they can determine why it was so virulent seven centuries ago when it doesn't seem to be so now.
    What if these geneticists are on the wrong path?  What if instead of studying why the bacterium seemed to be so virulent, they studied why the population of Europe in 1348 was so susceptible?

What if there were environmental factors from two or three generations before 1348 that made people particularly vulnerable to the Black Death?  The 14th Century was the tail end of the Middle Ages in Europe, and the early part of the century saw the Great Famine, which was about two generations before the Black Death.  Was there something about that calamity that turned on some DNA sequences - or turned some off - thereby predisposing certain people two generations later to contract the plague, and others to resist it?  I don't know, I'm not the geneticist, but I think it's worth exploring.

This has ramifications in modern day as well.  Aside from the obvious environmental toxins - like DDT and dioxin, which researchers are studying - there are many environmental stressors in modern society, and stress can do the epigenetic job just as well as chemicals.  Constant levels of stress can lead to increases in heart disease, liver problems, and obesity in people, but what else?  What changes are we making to our genes that we then pass onto our children?  Kind of a scary thought.