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In Chapter 25 of the book "To Kill a Mocking bird" Scout has caught a rolly polly. Jem tells her to put it out back. She is puzzled by his behavior because even though he has never been cruel to animals, he seems to be getting more and more concerned about insects. Scout wants to smash the rolly poly but Jem intervenes telling her that the rolly polly never did her any harm. In response to his behavior she thinks to herself;
"Jem was the one who was getting more like a girl everyday, not I."(239)
Scout equates attributes such as compassion for creatures as a feminine quality. Jem's resistance to harm the creatures validates her expression that Jem's behavior has become more feminine in nature.
One major theme of TKAM is coming-of-age, for both Scout and Jem. Earlier in the book, when Jem and Dill plot to leave a note for Boo Radley by putting it on the end of a stick and poking it through his window, Scout objects. She thinks it is dangerous to attempt to communicate with the town fiend in broad day light, especially after Atticus' admonishes the children to leave Boo alone. Jem tells her she is becoming "more like a girl" when she expresses her reluctance to get involved in the boys' scheme. Much later in hte summer, when Scout says Jem is becoming more like a girl, it is in response to his instruction to her to not harm a roly poly bug when they are sleeping on the porch. Scout does not understand that throughout the summer, as a result of Tom Robinson's trial and verdict, Jem has come to understand something about the people in his community. They are capable of prejudice and will send an innocent man to jail because he is black and his accusers are white. Jem learns that not everyone or everything can defend one's self in a world that is not always fair. Jem's epiphany is the result of many of his experiences--related to Tom Robinson's trial and to Boo Radley--and blossoms slowly as the summer progresses. In Scout's eyes, Jem's newfound compassion for weaker people/creatures is a weakness. However, as she narrates as an adult looking back, she does come to understand Jem's transformation, even if she did not entirely understand at the time.