Naturalism
When Gemmy leaves his aboriginal life behind, he brings with him a view of nature that offends the Europeans. Simply put, Gemmy feels that nature is not a thing to be dominated, since he perceives himself to be a part of nature, like the rest of the animals. This idea makes Gemmy a "savage" and a threat to their European way of life.
Xenophobia
Xenophobia is the fear of foreigners. The novel depicts xenophobia to be a kind of aversion to strange people, based in fear. The basic development is that some people are enlightened by the outsider's perspectives, and the rest are terrified. The more pessimistic group then exacerbates their paranoia by arguing without coming to a conclusion, and then they attack the outsider. This basic unfolding of xenophobia into blatant violence and racism is one of the most powerful thematic features of the novel.
Critiquing European colonialism
By allowing the reader to see the dark side of European colonialism, the author makes the reader reconsider their assumptions about society. Perhaps the effects of colonialism are not gone. This is suggested in the finale of the novel when the community mistreats a German because of the war in Europe. In other words, the insider/outsider attitude that colonial Europeans felt toward the native people continued into the future, so that now the community rejects foreigners in general, not just aboriginal people.
