Evolution of human intelligence: the roles of brain size and mental construction

Two competing philosophical paradigms characterize approaches to the evolution of the human mind. One postulates continuity between animal and human behavioral capacities. The other assumes that humans and animals are separated by major qualitative behavioral and mental gaps. This paper presents a continuity model that suggests that expanded human mental capacities primarily reflect the increased information processing capacities of the enlarged human brain including the enlarged neocortex, cerebellum, and basal ganglia. These increased information processing capacities enhance human abilities to combine and recombine highly differentiated actions, perceptions, and concepts in order to construct larger, more complex, and highly variable behavioral units in a variety of behavioral domains including language, social intelligence, tool-making, and motor sequences. Environmental input, including self-generated input, interacts with mental constructional capacities to assure that developing humans acquire species-typical and culturally-specific behavioral patterns. This mental constructional model is compatible with our current understanding of differences between human and non-human primate brains, of human brain plasticity, and of the minimal genetic differences between humans and chimpanzees.