The Plains of Passage continues and expands the themes of racism and sexism developed in the earlier novels.

As The Mammoth Hunters (1985) showed a Cro-Magnon community coming to accept and care for a Neanderthal boy, The Plains of Passage depicts more interaction between the two types of humans, this time on an adult level. The Cro-Magnons who hate the Neanderthals are portrayed as irrational bigots, and the Cro-Magnon communities band together to capture and punish their own people who attack and rape both Cro-Magnon and Neanderthal women.

As Jondalar and Ayla save a Neanderthal husband and wife who are being attacked by the Cro-Magnon gang, Jondalar learns that "flatheads," although different in appearance and customs, are human. Auel reveals her own dream of communities without prejudice when she writes of plans for Neanderthal and Cro-Magnon communities trading and working together to eradicate criminal activities and when...