Gordon Willard Allport (1897-1967) was an American psychologist and professor at Harvard, as well as one of the founding figures of personality psychology.
He writes in the Preface to this 1958 book, "The present volume does not pretend to deal with the science of human relations as a whole. It aims merely to clarify one underlying issue---the nature of human prejudice. But this issue is basic, for without knowledge of the roots of hostility we cannot hope to employ our intelligence effectively in controlling its destructiveness."
Here are some quotations from the book:
"Perhaps the briefest of all definitions of prejudice is: thinking ill of others without sufficient warrant." (Pg. 7)
"(W)e note an almost universal principle in respect to overlapping group differences: the diffences within the same group are greater (i.e., the range is wider) than the differences between the averages of the two groups." (Pg. 102)
"Now, what are the facts? Do Negroes, for example, have a distinctive body odor or not? ... (in an experiment) the offensiveness seems to come equally from the sweaty bodies of the two races. Odor is a curious psychological shibboleth. It is made to bear the brunt of intimate subjective feelings (and prejudices), but its role seems primarily to be that of an 'objective' excuse or rationalizer for affective states that are too personal and private to be understood or analyzed in their own right." (Pg. 135-136)
"Even those who favor segregation do not want Negroes to develop their own language or their own laws. They want they to be amalgamated in certain respects. And even those who argue for assimilation may wish to preserve certain pleasant cultural traits---perhaps the cuisine of the French, Negro spirituals, Polish folk dances, St. Patrick's Day." (Pg. 231-232)
"(A)bout a half of all prejudiced attitudes are based only on the need to conform to custom, to let well enough alone, to maintain the cultural pattern." (Pg. 272)
"(N)ot every American experiences the dilemma as (Gunnar) Myrdal defines it (in An American Dilemma: The Negro Problem and Modern Democracy (Black and African-American Studies) Volume 1). But many do. the theory, therefore, is valid enough if we take it to mean that often (but not always) prejudice is attended by mental conflict." (Pg. 315)