Maslow believed that human development occurs in five stages; at each stage we concentrate on mastering a different set of needs. The stages are physiological needs, safety needs, belonging needs, esteem needs, and self-actualization. The evidence Maslow presented for his theory consisted of personal observations and interviews of people he judged to be "self-actualized." His theory was evaluated by a number of researchers who began sympathetic to his viewpoint. The near-consensus view among researchers was that his theory is mostly invalid. Needs do not group into Maslow's categories and there is no hierarchy of needs common to the species. If there were, we would all have the same values.
Although there have been many lists of needs, the overlap is actually substantial. Except for his motive of self-actualization, Maslow's list of needs is similar to what many other psychologists recognized as needs. One of Maslow's main contributions was to group the needs into categories, which he did based on perceived common consequences. It is, of course, an error in logic to group motives based on consequences rather than intent. Maslow's other main contribution was the construct of self-actualization, which when all is said and done, is a substantial idea relevant to human transcendence, which during Maslow's career was a popular topic in existential philosophy and in theology.
I have been accumulating scientific evidence on the validity of a taxonomy of 16 basic desires. (A need is a universal goal common to the species; needs motivate everybody, but not in the same way. A basic desire is the subjective experience of a need.) I have collected data on many thousands of people from three continents. I have connected the 16 basic desires to personality traits, personality tests (Big 5, Myers Briggs), business coaching, school motivation, world-class & high school sports, relationships, anxiety disorders, developmental disabilities, media, and religion. I have published peer reviewed evidence of construct validity, reliability, concurrent validity, and criterion validity.
Although Maslow once wrote that he could not imagine how he could study his theory scientifically, actually questionnaires work well as measures of motives and needs. I am sometimes asked about defensive reactions to questionnaires. This question arises from the study of traits and is less relevant to the study of motives. A trait psychologist might ask people if they are smart, while a motivation psychologist asks people if they want to be smart or how much are they are impressed with smart. On a motivation questionnaire, people get any result they want by answering the questions in a straightforward and honest manner. They tend to be enthusiastic, not defensive.
Maslow's hierarchy does not exist. Generally, the strength of total motivation rises throughout the adolescent years and peaks around ages 25-35. After that it is mostly downhill as the intensity of the desires decline. The physiological desires decline much more rapidly than do the psychological desires. Fear is the only desire that rises in later years, perhaps because of the fear of death.
Maslow's ideas on human development, as well as evolutionary theory revisions of his ideas, are fairy tales. Advancing years bring decline, sickness, and eventually death, not self-actualization or great parenting. Youth brings passion about everything, not just physiological needs.
Maslow greatest mistake, repeated in evolutionary revisions of his work, is that he underestimated individuality. Everybody is motivated by the 16 basic desires, but people prioritize them differently. Every person has his or her own hierarchy, which is highly correlated to normal personality traits and intrinsically held values. A powerful predictor of behavior in natural environments is how a person prioritizes the 16 basic desires. This seems highly correlated to individual differences in rates at which desires satiate and renew their motivational strength.
An individual's prioritizations of needs is stable throughout the adult years. Although all desires are rising in adolescence and falling with advancing age, the relative prioritizations, and thus the person's values, are steady.
I recommend Maslow's work for the construct of self-actualization, which is a deep and interesting idea. Philosophers and theologians have been pondering human transcendence for centuries, and Maslow offered a novel perspective. The rest of Maslow's work, especially the hierarchy, is simply not true. Maslow should be read as a philosopher of human nature, not as a scientist concerned with data and validity.
(Anyone interested in practical applications of theories of needs should check out the upcoming annual conference of the World Society, at www.motivationscience.org).
