Black people are persons who differ from white people. The search can only lead to the most influential texts in human civilization-Bible, Koran, Torah, Talmud, etc., etc. The intrinsic circularity of gender, racial, and ethnic identities is obvious. White people, Gentiles, men, and heterosexuals are defined with reference to the their differences from black people, Jews, women, and homosexuals, respectively. Whites people are persons who have no black blood, and one drop of black blood makes the difference from whiteness.
Black blood marks a deviation from the order of whiteness.
Women are different from men. However, women are as different from women as men are different from women, and from other men. It has been observed that males and females have different pairs of identical chromosomes. There are differences between any two individuals or groups. Each individual is unique.