Frugivory

Eating fruits as preferred foods is common within the Primate Order and particularly among extant hominids. One hypothesis explains the relatively large brains in primates as due to requirements of locating and remembering clumps of or single fruiting trees across multiple annual cycles including variable amounts of available ripe fruit. A focus on non-fruits involves specific adaptations. The Old World subfamily colobinae and the New World genus Alouatta have expanded foreguts devoting more space to bacterial colonies, which enhance fermentation of leaf fiber. One colobine genus, the Duoc langur also has a gene duplication for a pancreatic enzyme, that specifically breaks down single-stranded bacterial RNA giving access to needed nitrogen. Hominids apparently lack such genetic adaptations; but gorillas, chimpanzees, and orangutans have expanded colons compared with humans enabling more extensive fermentation of fiber than in humans. Gorillas can meet energy needs eating herbaceous vegetation whereas humans and chimpanzees cannot. Hominids generally prefer ripe fruits; baboons successfully compete with hominids in Africa by taking fruits before they are ripe. Many of the fruits taken by hominids are high in fiber, particularly those eaten by orangutans during the dry season. Fermentation in their large colons permits energy extraction that is unavailable to humans. Emphasis on fermentation may limit energy output by individual hominids; a complication avoided by humans eating diets lower in fiber and higher in energy density and in nitrogen.