The latest research points to primarily sugar being the main problem in our diets. Excessive carbs in general seem to be likely driving a fair amount of weight and health problems and my very rudimentary understanding of the paleo approach addresses this and it's why many people on it find success -- if you're eating paleo, you aren't eating much bread, sugar, etc.
It seems to me that this transition to carb heavy diets that satiate hunger probably helped accelerate civilization -- it helped to satisfy hunger more easily and freed people to pursue activities that didn't involve hunting for food from dusk till dawn. But this came at a price -- negative health effects.
Maybe I just don't understand what paleo is all about, but trying to achieve a balance of macronutrients closer to those original diets seems like the point (or it should IMO) and not actually trying to eat foods that are 100% like what our ancestors ate.