Aunt Alexandra's answer to everything in To Kill a Mockingbird seems to deal with heredity. The Finch family ranked at the top of Alexandra's "caste system," and all other families fell somewhat lower.
She never let a chance escape her to point out the shortcomings of other tribal groups to the greater glory of our own...
There were hereditary Streaks, and every family in Maycomb had one:
... a Drinking Streak, a Gambling Streak, a Mean Streak, a Funny Streak.
There were Fine Folks, though Scout and her aunt disagreed on the interpretation of the term. To Scout, Fine Folks were "people who did the best they could with the sense they had." But to Alexandra, Fine Folks were determined by how long "a family had been squatting on one patch of land..." Scout seemed to agree with some of her Aunt Alexandra's thinking: Older folks "were utterly predictable," and most of the people's quirks and attitudes were simply handed down from a previous generation of the family, each "refined by time."