When Bob Ewell testifies, the reader learns that he is a coarse and uneducated man.
Bob Ewell’s full name is “Robert E. Lee Ewell, demonstrating his family’s preference for the Confederate side of the Civil War and labeling him as a racist. He is arrogant and rude. As Scout watches him be sworn in, she describes what she knows about the Ewell family.
[They] lived as guests of the county in prosperity as well as in the depths of a depression. No truant officers could keep their numerous offspring in school; no public health officer could free them from congenital defects, various worms, and the diseases indigenous to filthy surroundings. (ch 17)
All Ewells grew up deprived, and her father is used to it. When asked if Mayella is his daughter, he offends the judge and court by answering that if she isn’t there is nothing he can do about it.
We also learn that Mayella tried to keep some sense of beauty around, because she planted flowers. This shows that Mayella is not like the other Ewells. She is the one taking care of the children, and the one who is lonely.