The relationship between life span and medical (and dental) progress is not a very strong one. Although great strides have been made in combating some forms of infection, auto-immune diseases still kill the majority of people in the world. Other areas of technological innovation may have added more years to our life indirectly. A natural human diet consists of meats, fruits, vegetables edible raw, nuts and berries. All of these are much more common in the average persons diet because of the invention of the railroads and refrigeration. The increases seen in life span seem to follow these innovations more closely than any other factors. Before these were invented people ate more non-primate foods such as grains, beans, potatoes, milk products(such as cheese)and sugars which are less perishable. Thus only technology allows us to afford a "stone age diet"! Ray Audette Author "NeanderThin: A Caveman's Guide to Nutrition" http://www.sofdesign.com/neander