This study investigates the patterns of molar wear in hunter-gatherers and agriculturalists to test the hypothesis that there are systematic differences in tooth wear patterns related to differences in subsistence and food preparation methods. The flatness of molar wear is compared between five groups of hunter-gatherers (N = 298) and five groups of early agriculturalists (N = 365). Hunter-gatherers are predicted to develop flatter molar wear due to the mastication of tough and fibrous foods, while agriculturalists should develop more oblique molar wear due to an increase in the proportion of ground and prepared food in their diet. A method for quantitatively measuring and analyzing the flatness of molar wear is presented. Wear plane angles are compared between teeth matched for the same stage of occlusal surface wear, standardizing all groups to the same rate of wear. Agriculturalists develop highly angled occlusal wear planes, with angles exceeding those of hunter-gatherers by about 10° in advanced wear. Wear plane angles are similar within subsistence divisions despite regional differences in specific foods. The study uses a wide range of human groups, including Neolithic Europeans, prehistoric and early historic Nubians, early historic British, Mississippian American Indians, Puebloan American Indians, Middle and Upper Paleolithic samples from Europe and the Near East, Mesolithic sample from France, Archaic American Indians, recent Australian aborigines, and precontact Canadian and Alaskan Eskimos. The results show that hunter-gatherers maintain relatively flat, even wear at an advanced stage of tooth wear, while agriculturalists develop more oblique wear planes. This difference is attributed to a reduction in food toughness or fibrousness associated with the adoption of intensive grain collection and the use of grinding stones and pottery in food preparation. The study concludes that the flatness of molar wear is a good indicator of changes in food or food preparation methods, providing valuable evidence for dietary inferences in cultural and technological evolution in humans and early hominids.This study investigates the patterns of molar wear in hunter-gatherers and agriculturalists to test the hypothesis that there are systematic differences in tooth wear patterns related to differences in subsistence and food preparation methods. The flatness of molar wear is compared between five groups of hunter-gatherers (N = 298) and five groups of early agriculturalists (N = 365). Hunter-gatherers are predicted to develop flatter molar wear due to the mastication of tough and fibrous foods, while agriculturalists should develop more oblique molar wear due to an increase in the proportion of ground and prepared food in their diet. A method for quantitatively measuring and analyzing the flatness of molar wear is presented. Wear plane angles are compared between teeth matched for the same stage of occlusal surface wear, standardizing all groups to the same rate of wear. Agriculturalists develop highly angled occlusal wear planes, with angles exceeding those of hunter-gatherers by about 10° in advanced wear. Wear plane angles are similar within subsistence divisions despite regional differences in specific foods. The study uses a wide range of human groups, including Neolithic Europeans, prehistoric and early historic Nubians, early historic British, Mississippian American Indians, Puebloan American Indians, Middle and Upper Paleolithic samples from Europe and the Near East, Mesolithic sample from France, Archaic American Indians, recent Australian aborigines, and precontact Canadian and Alaskan Eskimos. The results show that hunter-gatherers maintain relatively flat, even wear at an advanced stage of tooth wear, while agriculturalists develop more oblique wear planes. This difference is attributed to a reduction in food toughness or fibrousness associated with the adoption of intensive grain collection and the use of grinding stones and pottery in food preparation. The study concludes that the flatness of molar wear is a good indicator of changes in food or food preparation methods, providing valuable evidence for dietary inferences in cultural and technological evolution in humans and early hominids.