We report data using an ape model to reconstruct the nutrient composition of the frugivorous diet of our last common ancestor with African great apes. We aimed to determine whether the African ape clade, from which hominids evolved, has any unusual features. We studied frugivory by comparing chimpanzee diets to that of three species of cercopithecine monkeys in Kibale Forest, Uganda.

Data came from a 12-month period that showed inter-monthly variation in fruit abundance. The monkeys consumed stable nutrient levels except for lipid, which was low (3.2 +/- 2.0 % dry matter (DM)), but peaked at about 9% DM during ripe fruit abundance. Chimpanzees also consumed low lipid and sugar diets during fruit poor seasons. Protein intake reflected each species' fallback food: leaf consumption kept the protein levels high for mbnkeys (16.7 +/- 1.9% DM); chimpanzees relied on herbaceous piths and maintained a low protein intake (9.5 +/- 3.0% DM). Fallback food was probably also responsible for the high fiber (NDF) intakes by monkeys, which was not significantly different from chimpanzees' (32.4 +/- 3.6% NDF versus 33.6 +/- 4.5% NDF respectively).

Three conclusions emerge: fat intake was low for all frugivores, protein intake was low for chimpanzees, and fiber intake was high for all species. Our data (from a lipid-poor habitat) show that high lipid or high protein is not needed for normal health and reproduction of chimpanzees. Therefore, hominids were probably capable of living on a low-fat, low-protein diet such as would be provided by fibrous roots commonly found in a seasonal woodland environment.