In 1943, a psychologist named Abraham Maslow published a paper on his theory of human motivations. My wildly over-simplistic explanation of his theory is that people will pursue meeting the most basic human needs before moving on to fulfilling more complex needs. We hunt and gather before we desire interpersonal relationships and professional respect. I learned about Maslow’s hierarchy in college, applied to the theory of how people spend (I majored in marketing). These days, I think more about how Maslow’s little pyramid applies to getting Tim through the day.
The theory is that people cannot progress to higher, more complex levels of interaction with society until the needs at lower levels of the pyramid are met. There are five levels in total. At the bottom are the physiological needs – food, sleep, breath. Level two focuses on safety – personal security, health, and livelihood. Three is called love and belonging, where friendships and intimacy reside. Level four is the more increasingly complex esteem level of confidence, respect, and personal achievement. The very top is self-actualization, defined as creativity, spontaneity, and acceptance of established facts. Maslow felt that a person not only could not progress to higher levels until the lower levels were met, but that persons would regress back to lower levels if deprived of a lower need.
http://psychology.about.com/od/theoriesofpersonality/a/hierarchyneeds.htm