Ungar describes how a tooth's "foodprints"--Distinctive patterns of microscopic wear and tear--provide telltale details about what an animal actually ate in the past. These clues, combined with groundbreaking research in paleoclimatology, demonstrate how a changing climate altered the food options available to our ancestors, what Ungar calls the biospheric buffet. When diets change, species change, and Ungar traces how diet and an unpredictable climate determined who among our ancestors was winnowed out and who survived, as well as why we transitioned from the role of forager to farmer. By sifting through the evidence--and the scars on our teeth--Ungar makes the important case for what might or might not be the most natural diet for humans.