The rationale for the Paleolithic diet derives from proponents' claims relating to evolutionary medicine.:594 Advocates of the diet state that humans were genetically adapted to eating specifically those foods that were readily available to them in their local environments. These foods therefore shaped the nutritional needs of Paleolithic humans. They argue that the physiology and metabolism of modern humans have changed little since the Paleolithic era.:594–95 Natural selection is a long process, and the cultural and lifestyle changes introduced by western culture have occurred quickly. The argument is that modern humans have therefore not been able to adapt to the new circumstances. The agricultural revolution brought the addition of grains and dairy to the diet.
A number of randomized clinical trials have compared the paleo diet to other eating plans, such as the Mediterranean Diet or the Diabetes Diet. Overall, these trials suggest that a paleo diet may provide some benefits when compared with diets of fruits, vegetables, lean meats, whole grains, legumes and low-fat dairy products. These benefits may include: