 His early work was on the Later Stone Age of East Africa, where he developed methods and ideas to study the landscape distributions of artefacts, giving rise to the sub-field of Off-Site Archaeology.In his work on human evolution he has emphasized an evolutionary ecological approach, seeing human adaptations as solutions to the problems faced by hominins in the environments in which they were living.This evolutionary research has also explored the relationship between climate and evolutionary change, the evolution of social behavior (finite social space model), and patterns of hominin diversity.