"I certainly never heard of that happening when I was growing up in the 30's and 40's."

Nor did I. (40s and 50s in my case).But that doesn't mean it may not have happened. It's very hard to be sure whether the fact that we read about something in the paper more often these days it's because it happens more often, or because the papers pick up on it more, even when it happens round the other side of the world. Bigger papers (and other media) with more space to fill in between the adverts affect the way we see the world.

I think we just don't know. It could indeed be that other changes in the way we live have cut away some of the things that could have made this kind of thing less likely, and I think that is quite probable. It would be very valuable to have people with the right skills seriously investigating questions like that, without preconceptions about the result they want to find.