Wild primates take most of the daily diet from plant sources,
eating moderate to small amounts of animal source foods (ASF).
Plant materials make up from 87% to >99% of the annual diet of
great apes, the closest living relatives of modern humans (Homo
sapiens sapiens). Reflecting their close genetic relationship,
gut form and nutrient requirements of apes and humans
(Hominoidea) are very similar, as is their pattern of digestive
kinetics—one predicated on a relatively slow turnover of
ingesta. In plant-eating mammals, in contrast to carnivorous
mammals, greater body size is associated with lower dietary
quality. Turning to ASF as a routine rather than occasional
dietary component would have permitted the evolving human
lineage to evade the nutritional constraints placed on body size
increases in apes. Without routine access to ASF, it is highly
unlikely that evolving humans could have achieved their
unusually large and complex brain while simultaneously
continuing their evolutionary trajectory as large, activ