Question: why is there a black baby on this is us

title: One-drop rule
text: The one - drop rule and its consequences have been the subject of numerous works of popular culture . The American musical Show Boat ( 1927 ) opens in 1887 on a Mississippi River boat , after the Reconstruction era and imposition of racial segregation and Jim Crow in the South . Steve , a white man married to a mixed - race woman who passes as white , is pursued by a Southern sheriff . He intends to arrest Steve and charge him with miscegenation for being married to a woman of partly black ancestry . Steve pricks his wife 's finger and swallows some of her blood . When the sheriff arrives , Steve asks him whether he would consider a man to be white if he had `` negro blood '' in him . The sheriff replies that `` one drop of Negro blood makes you a Negro in these parts '' . Steve tells the sheriff that he has `` more than a drop of negro blood in me '' . After being assured by others that Steve is telling the truth , the sheriff leaves without arresting Steve .