What does Jem say to point out the irrationality of Aunt Alexandra's major theory concerning human behavior in Harper Lee's To Kill a Mockingbird?

Early in her stay with the Finches in Harper Lee's To Kill a Mockingbird, Aunt Alexandra tries to teach the children her prejudiced views about hereditary human behavior. In Aunt Alexandra's mind, all human failings can be attributed to heredity. Specifically, she argues all of Maycomb's people have negative streaks they inherited from their families:

Everybody in Maycomb, it seemed, had a Streak: a Drinking Streak, a Gambling Streak, a Mean Streak, a Funny...

Early in her stay with the Finches in Harper Lee's To Kill a Mockingbird, Aunt Alexandra tries to teach the children her prejudiced views about hereditary human behavior. In Aunt Alexandra's mind, all human failings can be attributed to heredity. Specifically, she argues all of Maycomb's people have negative streaks they inherited from their families:

Everybody in Maycomb, it seemed, had a Streak: a Drinking Streak, a Gambling Streak, a Mean Streak, a Funny Streak (Chapter 13).

She further defines being good people, or "Fine Folks," as having a strong heritage. The longer a certain family lived on its land, the finer the family was. The finer the family, the better their behavior was. She uses this logic to claim the Finches are the best of people because they are "Fine Folks" who own their farm, Finches Landing.

Jem contradicts her argument that established residency makes a family fine by pointing out, "That makes the Ewells fine folks" (Chapter 13). The Ewells are the exact opposite of fine folks because they are uneducated, alcoholics, refuse to work, and live off of welfare. Jem's comment serves to underscore how wrongfully prejudiced Aunt Alexandra's views are.

After Tom Robinson's trial, Jem comes to understand that his aunt's views about the fineness of people has more to do with education. Jem interprets his aunt's statements about "Old Family" as meaning that the longer "your family's been readin' and writin," the better your family is, which is why Aunt Alexandra sees the Finches as being of higher standing than other families (Chapter 23). Jem uses his understanding of his aunt's comments to explain why everyone is different and why different people hate each other so much.