Food is the body's fuel ,now a study finds the amount of the energy in that fuel can depend not just on it's calorie content but on how it's prepared,and the research published in the proceedings of the National Academy of Sciences could explain an inch leaping human evolution .Food's energy value is usually measured beofore consumption ,but Harvard scientists bet two groups of mice,either meat or sweet potatos and prepared them differently .Either whole of panned ,raw or cooked to create variety of diets .The reserchers then measure the mice,found that panned meat and potatos cause more wieght gained than raw food. Cookie increses the weight most.The extra calorie cookie makes available may have allowed the suviral humans with larger bodies and more comllex brains.studying almost 2 million years ago, those physical changes are required more energy and explosing food to fire may have provided that boost. Of course a legacy revolution is that modern humans often gain too much wieght which might be called a raw deal .