The evolution of intelligence: adaptive specializations versus general process

Darwin argued that between-species differences in intelligence were differe nces of degree, not of kind. The contemporary ecological approach to animal cognition argues that animals have evolved species-specific and problem-sp ecific processes to solve problems associated with their particular ecologi cal niches: thus different species use different processes, and within a sp ecies, different processes are used to tackle problems involving different inputs. This approach contrasts both with Darwin's view and with the genera l process view, according to which the same central processes of learning a nd memory are used across an extensive range of problems involving very dif ferent inputs. We review evidence relevant to the claim that the learning a nd memory performance of non-human animals varies according to the nature o f the stimuli involved. We first discuss the resource distribution hypothes is, olfactory learning-set formation, and the 'biological constraints' lite rature, but find no convincing support from these topics for the ecological account of cognition. We then discuss the claim that the performance of bi rds in spatial tasks of learning and memory is superior in species that dep end heavily upon stored food compared to species that either show less depe ndence upon stored food or do not store food. If it could be shown that sto ring species enjoy a superiority specifically in spatial (and not non-spati al) tasks, this would argue that spatial tasks are indeed solved using diff erent processes from those used in non-spatial tasks. Our review of this li terature does not find a consistent superiority of storing over non-storing birds in spatial tasks, and, in particular, no evidence of enhanced superi ority of storing species when the task demands are increased, by, for examp le, increasing the number of items to be recalled or the duration of the re tention period. We discuss also the observation that the hippocampus of sto ring birds is larger than that of non-storing birds, and find evidence cont rary to the view that hippocampal enlargement is associated with enhanced s patial memory; we are, however, unable to suggest a convincing alternative explanation for hippocampal enlargement. The failure to find solid support for the ecological view supports the view that there are no qualitative dif ferences in cognition between animal species in the processes of learning a nd memory. We also argue that our review supports our contention that specu lation about the phylogenetic development and function of behavioural proce sses does not provide a solid basis for gaining insight into the nature of those processes. We end by confessing to a belief in one major qualitative difference in cognition in animals: we believe that humans alone are capabl e of acquiring language, and that it is this capacity that divides our inte lligence so sharply from non-human intelligence.