There's a much simpler explanation for the declining health of successive generations and the increases in chronic illnesses. Before the advent of modern medicine, only the naturally strong survived to adult-hood. Children born with anything that compromised their immune system and overall health, such as food intolerances or even allergies, mostly died. My grandmother was fiercely healthy into her 80s, which is no surprise since she was strong enough to survive scarlet fever, mumps, measles, and probably a few other now-prevented diseases I don't know about. 6 of her 14 siblings failed to survive these illnesses. Today those 6 children would probably survive to pass on their weaker genetics.

People don't like this explanation, but we're now looking at as many as 4-5 generations that have been influenced by modern medicine, each experiencing a greater influence than the last. And not only do those who would've died in earlier eras survive, but people with chronic illnesses, including mental illness, receive treatment that improves their quality of life--making it more likely they'll have children and pass on the propensity for compromised health. This is painfully obvious in my mood disorder support group. Most of their children also have mood disorders, as do a lot of their parents and siblings.

This isn't even really a theory. It's a proven fact that one of the greatest risk factors for mental illness is genetics. It would be nice to think that there was some environmental factor we could blame, because environmental factors can be changed, but I've never seen a credible study that changing what you eat will cure or even treat bipolar disorder.