A Paleolithic-style diet, popularly known as a Paleolithic diet, paleo diet, caveman diet, Stone Age diet or hunter-gatherer diet, is a contemporary diet regime, consisting of commonly available modern foods, that emulates the diet of wild plants and animals that humans and their close relatives habitually consumed during the Paleolithic (the Old Stone Age), a period of about 2 million years duration, ending about 10,000 years ago, when Homo sapiens invented agriculture. Deriving from the field of evolutionary nutrition, this dietary concept is based on the premise that modern humans are genetically adapted to the diet of their Paleolithic ancestors and that human genetics have scarcely changed since the dawn of agriculture, and therefore that an ideal diet is one that would resemble such an ancestral diet.Proponents of this nutritional approach differ in their dietary prescriptions, but all agree that people today should eat mainly meat, fish, vegetables, fruit, roots and nuts, and avoid grains, legumes, dairy products, salt and processed fat and sugar. They argue that modern human populations subsisting on traditional diets similar to those of Paleolithic hunter-gatherers seem to be largely free of diseases of affluence, and that such diets produce beneficial health outcomes in controlled medical studies. Supporters point to several potentially therapeutic nutritional characteristics of preagricultural diets. Critics of this dietary approach have taken issue with its underlying evolutionary logic, and have disputed certain dietary prescriptions on the grounds that they pose health risks and may not reflect real Paleolithic diets. They also argue that such diets are not a realistic alternative for everyone, and that meat-based diets are not environmentally sustainable.