Introduction

According to Darwinian thinking, organisms are (for the most part) designed by natural selection, and so are (for the most part) integrated collections of adaptations, where an adaptation is a phenotypic trait that is a specialized response to a particular selection pressure. For animals that make their living in the Arctic, one adaptive problem is how to maintain body temperature above a certain minimum level necessary for survival. Polar bears’ thick coats are a response to that selection pressure (surviving in extreme cold). A thick coat makes a positive difference to a polar bear's fitness, since polar bears with very thin coats left fewer offspring than those with thicker coats. The foundational idea of evolutionary psychology is that brains are no different from any other organ with an evolutionary function, insofar as brains too are systems shaped by natural selection to solve adaptive problems. Thus brains have a particular functional organization because their behavioural effects tend, or once tended, to help maintain or increase the fitness of organisms with those brains. Prominent evolutionary psychologists (for example: Cosmides and Tooby, 1987 Cosmides and Tooby, 1994 and Symons, 1992) have endorsed the view that the last time any significant modifications were made by natural selection to the human brain's functional architecture, we were hunter-gatherers, inhabiting a world quite different from that which we now inhabit. That world was the Pleistocene epoch, between about 2 million years ago and 10 thousand years ago.