Introduction The evolution of human intelligence is one of the outstanding problems in the sciences of life and mind. It is a problem that so struck Alfred Russel Wallace, the codiscoverer of natural selection, that he categorically ruled out evolutionary hypotheses and invoked divine infusion as the source of higher cognition in humans. This turn by Wallace has become a paradigmatic illustration of the difficulty and fascination that attends the scientific investigation into the genesis of our extraordinary cognitive powers (Gould, 1980). Although in many ways as daunted as their great predecessor, few psychologists and human evolutionists today endorse Wallace's solution. In the modern context the problem appears to pose two aspects with an as-yet uncertain degree of interdependence. The first aspect addresses the species-universal architecture of human cognition and its antecedents in more basal systems (Pinker, 1997). The second aspect is concerned with quantitative differences among individuals along dimensions of cognitive abilities and changes in the distributions of the traits represented by these dimensions over the course of evolutionary time. This second aspect, however, has been less well explored by evolutionary psychologists and other workers concerned with the stated outstanding problem. The aim of this chapter with respect to this underdevelopment is twofold: (1) to propose possible resolutions to problematic issues that may to some extent be responsible for this relative neglect, and (2) to discuss future prospects for the integration of differential psychology into human evolutionary studies.