Our understanding of behavior has grown tremendously in the past several hundred years; however the majority of the advancements have been recent. Psychology, as sciences go, is one of the "new kids on the block". Philosophers of ancient Greece and Rome argued for hundreds of years about some of the same issues that psychologists consider today. The most well known philosopher of Ancient Greece was Aristotle. Aristotle compared human behavior to the movements of the stars and seas in that; both are subject to rules and laws. Socrates, another Greek philosopher, believed that humans should rely on rational thought and introspection.
The formal beginning of psychology has been set in the year 1879, when William Wundt established the first psych lab in Leipzig, Germany. His aim was to study the building blocks of the mind. Wundt founded the school of psychology known as structuralism. Structuralism argues that the mind consists of three basic elements: sensations, feelings, and images. Wundt believed psychology was the study of conscious experience, which broke down into two parts: objective sensations and subjective feelings.
At about the same time Wundt was establishing his lab in Leipzig, William James was setting up one of his own in Cambridge, Massachusetts. The main perspective that replaced structuralism as psychology grew is known as functionalism, founded by James. Functionalism concentrated on what the mind does and how behavior functions, rather than on the mind's components. Another perspective of psychology was the Behavioral perspective. Behaviorism was founded by Watson in the 1920s. Watson believed that one could gain a complete understanding of behavior by studying and changing the environment in which people lived in. B.F. Skinner and he looked for reinforcement patterns. Gestalt psychology, founded by Wertheimer, Koffka, and Kohler, was another reaction to structuralism in the early 1900s, focusing on how perception is organized.