The Evolution of Thought: Evolutionary reconstructions of great ape intelligence

Research increasingly shows great apes surpassing other nonhuman primates in their mentality, achieving abilities traditionally considered uniquely human. Importantly, the cognitive capacities that distinguish them include rudimentary symbolic processes, in the sense of processes that operate on the basis of mental images rather than direct sensory-motor phenomena. Although this view does not represent consensus among experts (e.g., Tomasello & Call 1997), many well-respected researchers now accept this interpretation of the empirical evidence (e.g., Byrne 1995; Langer & Killen 1998; Parker & McKinney 1999; Parker, Mitchell & Boccia 1994; Parker, Mitchell & Miles 1999; Russon, Bard & Parker 1996; Savage-Rumbaugh, Shanker & Taylor 1998; Whiten & Byrne 1991; Wrangham et al. 1994). If great apes are capable of symbolic cognitive processes, views of symbolism as having evolved within the human lineage are incorrect. Implications for understanding cognitive evolution within the primates are complex and important. First, neither the landmark significance of symbolism to cognition nor its importance in understanding the evolution of higher primate cognition is diminished by this revision. What is altered is timing. Symbolic cognition shifts from an achievement of the human lineage to a foundation for it. Second, reconstructions of the conditions leading to the evolution of symbolic processes remain important, but existing reconstructions lose much of their weight because they focus on conditions linked with the divergence of the human lineage. If symbolic processes are the joint province of humans and great apes, ancestral large hominoids are their probable evolutionary source. At this vastly different point in time and probably in space, a very different set of conditions likely affected them. Finally, what is unique to the human mind must be reevaluated. This volume aims to reconstruct the evolutionary origins of great ape intelligence. This is not the first such reconstruction; over half a dozen have been developed over the last 25 years, primarily by scholars of cognition (e.g., Byrne 1997; Byrne & Whiten 1988; Parker & Gibson 1977, 1979; Parker 1996; Povinelli & Cant 1995; Russon 1998). While their expertise on issues of cognition is undisputed, their navigation and rendition of evidence and debate in the other key areas can be less sound. Many extant reconstructions, for instance, rely on outdated or flawed views of modern great ape anatomical or behavioral adaptations, sociality, ecology, or ancestry (for discussion, see Byrne 1997, 2000; Russon 1998). Reconsidering the evolutionary origins of great ape intelligence is well worth undertaking at this time. The accumulation of empirical evidence is generating better models of cognitive processes in living great apes. The body of knowledge on the behavioral, anatomical, social, and ecological traits of living great apes is affording increasingly reliable identification of potentially conservative traits. A recent upsurge of interest in hominoid evolution occasioned by significant fossil finds and increasingly sophisticated molecular taxonomic methods enormously improves the prospects for honing in on the critical pieces of the ancestral hominoid picture that concern cognition. To orient our attempt, this first chapter revisits existing reconstructions of cognitive evolution that implicate the great apes. Aims are to highlight why and where evolutionary reconstructions of great ape cognition are in need of revision, the factors potentially at play, and our approach to developing a new reconstruction.