Human personality is the collection of complex characteristics and traits that shape and distinguish an individual from a machine-like object. The study of these traits and differences among individuals can be dated back centuries to the ancient Greek and Roman physicians and philosophers. Hippocrates applied the concept of humors to medicine, and the writings of Galen elaborated this concept for centuries. The humoral theory held that four bodily fluids or humors – black bile, yellow bile, blood, and phlegm – corresponded to four temperaments. This simple description of human characteristics was an early step toward what has become an expansive field exploring the complexities of personality in the context of philosophy, psychiatry, and neurology, and ranging from the molecular and cellular levels to the individual organism. Personality is defined as the dynamic organization of the psychobiological systems by which a person shapes and adapts in a unique way to a changing internal and external environment . In other words, personality describes the dynamic processes that occur within a person to allow behavior to shape and adapt to life experiences. The maturation and integration of human personality involves the development of habits and skills, learning facts and how to reason, and growing in self-awareness through experiences across a wide range of situations.