I forgot where I read it, but I saw this article with respect to that new documentary movie "Babies." The writer gave an analysis of how each baby was raised and where- and germs that they were susceptible too. For instance, the Namibia baby grew up around farm animals and likely built up a resistance to germs early on; whereas the baby in SF was more susceptible to germs due to being in a cleaner environment; and autoimmune diseases like Type 1 diabetes due to being around more chemicals- like pesticides and stuff. My mom grew up in the Phillippines and had no health probs except for anemia; my dad has nothing wrong w/ him and he grew up in LA, but his aunts and mom had hyper or hypo thyroid probs which are autoimmune diseases.
Anyway, I wish I could find the article- I'll try to google it. Please comment your thoughts or any knowledge of studies done on this subject.