There are many more complications to this topic than most folks realise, and research does not always find answers... often only more problems...
I'll use one as an example....
Some years ago an investigation into "clusters" of one type of cancer found that it occured where a certain type of rock (granite) was present. The results seemed to prove that radon - a radioactive gas - might be "seeping" from the rocks and causing an increased rate of cancer. The problem was... why was this occuring now, when folks had lived in these areas for many years without problems. Also, why did it not occur in other areas where the same rocks formations were present.
A theory was eventually produced that many said was rubbish ... that being that the cases of cancer were only appearing in "new build" areas and not older houses.
Some years later that theory was actually proved correct !! What actually happened was that in "old" houses the draughts and ill fitting doors/windows/thatched roofs the radon levels never built up. "Modern" houses with double glazing/central heating etc etc were actualy "trapping" the gases inside so the exposure of the occupants was increased.
The gas has not changed.. it has always been there.. and always will... but our "modern" way of live has changed the way we interact with it.. and now cancers form because of it.
My guess is.... the same is occuring in many other areas... for example ... processed foods now expose us to things we never met years ago ... preservatives/colourings/ "flavour enhancers" (?) etc etc.
I don't think the cancers are "man made" ... but possibly "man has increased the exposure" ....
