Teeth of the earliest known hominids are not very different from the teeth of Miocene hominoids. This suggests that the earliest hominid fed similarly to their hominoid ancestors, which resemble modern great apes. Consequently, comparative analysis of feeding ecology and diets of the great apes constitutes one route to reconstructing the baseline diet of the Hominidae. The last four decades have produced remarkably detailed descriptions of diets and feeding ecology of orangutans, gorillas, chimpanzees, and, more recently, bonobos. Various key observations may be relevant to understanding aspects of the human diet. For example, terrestrial herbaceous vegetation provides subsistence for the African apes when richer foods (fruits) are rare, and large body size facilitates digestion of such low quality, fibrous material. To the extent that early hominids were large (on the "mouse-to-elephant" scale), the interaction of body size and digestive capacity may be significant for understanding early hominid dietary potential. Although meat constitutes only a small part of the diets of apes, it is a consistent item in those diets. The rare, but socially charged, consumption of meat by chimpanzees may provide a second useful perspective on the earliest hominid diets. This paper presents comparative analysis of diets of the great apes and derives a few general conclusions about the boundaries of early human dietary adaptation, although facultative adaptation by apes to quite variable diets may confound this effort.