Maslow's hierarchy of needs is an idea in psychology proposed by Abraham Maslow in his 1943 paper "A theory of Human Motivation" in the journal Psychological Review. Maslow subsequently extended the idea to include his observations of humans' innate curiosity. His theories parallel many other theories of human developmental psychology, some of which focus on describing the stages of growth in humans. He then created a classification system which reflected the universal needs of society as its base and then proceeding to more acquired emotions. His theories, including the hierarchy, may have been influenced by teachings and philosophy of the Blackfeet tribe, where he spent several weeks prior to writing his influential paper.