I believe what WalkingDream is referring to is the carrying capacity of the earth. The carrying capacity is the number of humans the earth can support living moderately with neccesary resources. Current estimates range from 7 to 100 billion while some as walkingdream have stated believe we have already far exceded the carrying capacity. When he refers to oil I believe he is referring to fossil fuels which have fueled modern agriculture modern medicine travel heating and living in climates we normally would not etc. Your initial question is quite interesting and has crossed my mind as well. I too wonder what role modern medicine has in our evolution as humans. It's a strange concept to think about when you look at our earth and how we are eventually going to overpopulate it unless we eventually expand to other planets and without modern medicine would this be neccesary ? I'd be interested in what others have to say on this subject matter. Cool question haze.