Abraham Maslow posited a whole lot of things in the theory that is called Maslow's Hierarchy of Needs. Among the things that he posited was the progression from more "basic needs" like physiological needs and safety to more subtle needs such as self-esteem. Last but not least, he posited that there is a need for Buddha-like enlightenment, which he termed as Self Actualization, which transcended any actual need existing in the human being, and may actually cause him to jeopardize the attainment of his physical, psychological and social needs in quest of an undefinable something that holds greater meaning for him/her.
While all this agrees with out intuitive understanding of the seemingly universal human desire for greatness and causes that are "greater than oneself", it all smells suspiciously spiritualistic.
Psychology arguably being a science and not a part of "humanities" like, say, Economics, it may be expected to demand more rigorous proof in the form of truly independent peer-reviewed scientific studies to determine whether Maslow's Hierarchy of Needs is actually true of Homo Sapiens as a species, and not just a figment of our fond (and somewhat religiously inspired) imaginings that we are beings who have "fallen from grace".
So, what is the actual scientific proof of various aspects of Maslow's Hierarchy?