I think we just don’t know, really. It could be replacement of some sort - car usage has gone up continuously, and we inhale a lot of exhaust in cities. Maybe

I think we just don’t know, really. It could be replacement of some sort - car usage has gone up continuously, and we inhale a lot of exhaust in cities. Maybe it was exhaust the whole time? I’d also be interested to see the data you’re referencing on lung cancer rates in non-smokers.