Part A: Some people have this great love to learn everything. I know a math MA that studies relativity books for fun. A philosophy major that wants to study math so that he can learn about Godel ` s theorm. I know a girl that loves to cook, and she read every cock book, and try every recipe. I remember reading about James C. Maxwell study a whole bunch of mathematics in college from library books by himself. I also read in the biography that Einstein, and Newton were largely self-thought themselves their subject. Newton largely self-taught himself greek geometry in order to understand Descartes, and Kelper. Einstein self-taught himself classical electrodynamic theory because it was not taught in the university. They cannot be majority of the population. Part B: I try to look for profiles and classification of different personality types. What i found is that "myer briggs personality types" is most commonly used in personality tests by psychologists, and in carreer accessment tests. I am at all saying people can be classified. I am saying many people use it, so there might be some merits to the system. You can find information here: http://typelogic.com/index.html Part C: Of the different profiles in the above link. I try to find the type that most fit lifetime learners, and this type is INTP.Of the reasons that make me think self-learners tend to be INTP are the following descriptions of INTP: "Report 3 to 9 hours a week of non-required serious reading"( http://220.127.116.11/search?q=cache...non+required+reading&cd=1&hl=en&ct=clnk&gl=us) "The INTP is a relentless learner in areas that hold his or her interest. They often seem 'lost in thought,' and this characteristic appears very early. INTPs enjoy the life of the mind and the learning process, regardless of whether that process takes place in a formal sense. They are often characterized as life-long learners." ( http://community.livejournal.com/jmbt_intp/141558.html) Here is my argument: 1) The observation that there are many self-learners ( part A). 2) People can be categories by myer briggs personality types, therefore, INTP is a valid category ( part B). 3) MB intp descriptions tend to fit the profile of self-learners. (past C). 4) Self-learning tend to be most common in one of the M.B type, INTP( 1&3).