40 odd years ago one of my chosen subjects as part of my first degree was Demography. I remember from back then that one of the reasons there were more people dying of  cancer was that they were living long enough to get it..... Before, so many died earlier of childhood diseases, smallpox, polio, typhus, cholera etc..... after every breakthrough there was a drop in the mortality rate for a time!

This is not to say that modern living doesn't cause new illnesses, especially diabetes, heart ailments, certain cancers, obesity etc!