11 - Clever hands: the food-processing skills of mountain gorillas

Summary

The mentality of apes is often discussed as if it had no direct connection with their natural lives. Whereas behavioral ecology is studied by zoologists and set in relation to the foraging strategies of other species, mentality is seen as the province of psychologists and all too often studied only in the laboratory. An artificial and unhelpful divide for any species of animal, this partition is especially damaging for a proper understanding of the great apes. I will argue that the cognition of the great apes can only be understood in relation to their means of acquiring an adequate diet: that, in a very real way, great apes inhabit a “cognitive niche”. To set out and evaluate this proposal, it is essential to begin by considering the foraging choices available to the apes.

The ecological niche of the great apes

Large primates with simple stomachs have a stark choice, between plant foods which are relatively nutritious but costly to acquire, and those which are more readily available but of inferior quality (Waterman, 1984). Lacking morphological adaptations for carnivory, only the very smallest primate species – such as galagos, the smaller lemurs, marmosets and tamarins – are able to specialize on animal food (insects), in some cases supplemented by tree gum (Hladik, 1978). Only the colobine monkeys possess complex stomachs, enabling high-quality nutrition to be obtained from mature leaves via bacterial action (Chivers & Hladik, 1984). For the remainder of the primate order, there is limited room to maneuver. In general, plant items which provide abundant and readily available energy, especially simple sugars and lipids, tend to be sparsely distributed and short-lasting and so require considerable locomotor effort to obtain.