All normally functioning humans learn the basic requirements of social participation, but the rewards of a modern complex society go to those with the ability to most quickly and effi ciently assimilate a culture forever in fl ux and forever moving in the direction of broadening scope and deepening complexity. Human learning requires cognition, and cognition makes use of symbols-letters, words, pictures, formulas, and so on-that stand for various aspects of the environment and the relationships among them. Because of its increasing importance to success, the issue of differential ability becomes more and more socially relevant: “Intelligence has a profound effect on the structure of society, not necessarily because it is the most highly valued of individual differences-although conceivably it is-but rather because it may have the widest and most stable distribution among all the traits that are valuable in industrialized nations” (Gottfredson 1986: 406). Intelligence is more closely tied to class mobility in modern societies than any other single factor, but having said this we must not confuse intelligence with moral worth. As Herrnstein and Murray (1994: 21) point out: “one of the problems of writing about intelligence is how to remind readers often enough how little IQ scores tells you about whether the human being next to you is someone you will admire or cherish.”