What makes you “you”? This question gets to the heart of one of the longest-running debates in psychology: the nurture versus nature dispute, which asks whether humans are a product of their environment or of their biological makeup. While it is unlikely that we will ever conclusively answer this question, research has provided us with some important insights that will assist you in understanding arguments on both sides of the debate. This unit will then explore our neurological system especially the structure and functions of neurons as well as parts of the brain. Early psychologists considered the brain a “black box” that controlled certain processes, though they did not know how to identify these processes or how the brain controlled them. This is no longer the case; nowadays, scientists insist that the psychological mind and physiological body are fully integrated with one another. Today, knowledge of the biological origins of our psychological states is integral to the study of psychology.