What motivates people? Why do they behave as they do? For that matter, why do people do anything at all? Questions like these have persisted over 100 years of psychology despite decades upon decades of research to answer them. Waves of academic thinking have addressed these issues, with each new school of thought providing different answers, at least in form if not in function. In our brief overview of motivation theory, we will emphasize commonalities in theory rather than their differences. We will then discuss evolutionary theory as an overarching, modern model of motivation — specifically, the motivations to promote one’s survival and to be reproductively fit in a Darwinian sense. This discussion of evolutionary theory will be applied to human motivation and to the many ways in which people — such as ourselves — adapt in a complex world.