I believe what is meant by the notion is that prejudice, particularly in regards to race, is not present at birth, it generally has to be acquired through one's own "kin" or "kind". If this is to be taken LITERALLY, I have no freakin clue, I never heard such a thing before. Even on a METAPHORICAL level, I have no idea who said it first. Even metaphorically I have never heard such a notion being uttered by anyone or have I even read such a thing. But I believe my immediate interpretation is the correct one.