I feel that the theme in these lines has something to do with law, ruling, listening, obeying and being in charge.
A few quote examples to help support this theme is/are: "...girls usually side with their mother...."
"...her authority in the home shrank as my mother's authority gradually extended..."
"... the law of life..."
"...obey the law readily and willingly."
You may have approached the question in these ways:
explained how stories have been passed through generations
incorporated stories and myths based on historical and archeological information
mentioned the importance of these stories and traditions
included examples from the texts that support your ideas
mentioned the tone of Momaday’s writing and how it influences the reader’s perspective on the Kiowa culture