Each mountain ridge in this landscape has a distinct contour, with various peaks whose heights reflect evolutionary time. That is, within humankind's evolutionary landscape there are several naturally selected systems that contribute to channeling human experience toward religious paths. In the processing of human experience, these systems, and their components, interact and develop interrelated functions - as do geological, hydrological, and organic systems in the drainage process.

Introduction: an evolutionary riddle, p. 11 - In Gods We Trust: The Evolutionary Landscape of Religion (2002)