Its important to note how strongly Harper Lee demonstrates the effects of environment in this novel, particularly with reference to the Ewell family. Mayella can been seen in contrast with her father, as she shows feelings of tenderness, but she is still caught in a net of disgrace. To save herself, she allows an innocent man to be accused and convicted. She can not see past the behaviors that her father has instilled in her, despite her obvious desire to escape.
Similarly, Mayella's younger siblings demonstrate tendencies towards corruption. The offer no help to the eldest Mayella in her household duties, in favor of running about loose in town. The younger Ewell we meet in Chapter 2 is surly and rude, and shows no interest in gaining education and bettering himself, showing up only on the first day of school. Lee makes a critical statement about the effects of social pressure and social class upon the masses, a statement echoed by Atticus in his closing arguments, when he insists that all men have not been created and are not treated equally.
The Ewell family has been "the disgrace of Maycomb for three generations". Bob, the father, is a drunk with no job who provides almost no support to his large family. There have been rumors that he beats his children. He is uneducated and has no respect for any kind of authority. When Atticus questions him during Tom Robinson's trial, Bob becomes angry and resentful because Atticus exposes his true nature. Bob won't directly go after Atticus because he's a coward, so he attacks Scout and Jem and is subsequently killed by Boo Radley.
Mayella Ewell, the oldest daughter of Bob, keeps house for him and her seven brothers and sisters without any help from anyone. She is a lonely girl who has been abused by her father. She has no friends or anyone she can count on. She's never had a mother to help her. When Tom Robinson helps her do some things around the house, she tries to repay his kindness by seducing him. When her father discovers this, he beats her and forces her to accuse Tom of rape. Even though the Ewells are considered white trash and the worst family in town, Tom Robinson is convicted of Mayella's rape.