Caton / Poster
The hominoid digestive strategy
Judith M. Caton
The diets of extant hominoids, which are plant-based, contain
appreciable amounts of non-starch polysaccharides that require microbial fermentation
before they can be used as an energy source. Hominoids use the digestive strategy of colon
fermentation for processing the non-starch polysaccharide component of their diets.
The diagnosis of digestive strategy is based on three groups of
data* wild diet, gastro-intestinal morphology and digesta passage experiments. Hominoid
diets consist of ripe fruit, young leaves, and other plant parts, supplemented with a
range of animal foods. Human hunter-gatherers eat similar diets. The morphology of the
gastro-intestinal tract has a common pattern in all hominoids: a unipartite stomach, a
long, narrow small intestine, a small caecum ending in a vermiform appendix, and a colon
divided into proximal and distal segments. The musculature of the hindgut is complex as it
is adapted for mixing and retaining digesta for microbial fermentation.
Microbial fermentation is a much slower process than enzymatic
digestion, thus digesta passage through the guts of plant-eaters is much slower than for
mammals eating diets requiring no fermentation. A fluid and a particle marker are used to
measure the rate of digesta passage from mouth to anus. The results of these studies with
hominoids demonstrated that there was prolonged retention of digesta both markers in all
species, with the particle marker being retained for longer than the fluid marker. This
pattern of marker elimination from the guts of apes is consistent with that recorded from
other plant-eaters using the digestive strategy of colon fermentation.
The three-pronged approach to the study of extant primate
digestive strategies incorporating ecological, morphological and physiological data is a
means of providing new and valuable insights into the digestive strategies of closely
related species, e.g. Homo erectus and Homo sapiens. Walker and Shipman, (1996) discussed
the conclusion, based a skeleton exhibiting symptoms of hypervitaminosis A, tooth
microwear and the Expensive Tissue Hypothesis* of Aiello and Wheeler (1993) that H.
erectus was a carnivore. Similarities in gut morphology and the common digestive strategy
of the hominoids suggest that this was unlikely, and that H. erectus was an opportunistic
scavenger, supplementing its diet with animal foods when available.