The name-changing captain
The captain is a person who changes his own name frequently. This is a symbol for his shame, because he is a person with a contemptible job. He kidnaps endangered animals and sells them in the black market, so perhaps his changing name is a symbol for his shifty identity and the way he can't bear to look at himself honestly. This character represents shame.
Erasmus as a symbol
To say Erasmus is a character is a little confusing, because he does seem to be a character, but that is also the major dilemma of the story, whether he counts as a character or not. He is a symbol for the dilemma between humanity and animal instinct. As an informed theologian, Erasmus is a thinker and an intuitive philosopher, which is the best of what the humanities offer, but he is also purely ape-like. He is an animal. In other words, he is a plot device that lets the readers consider their own animal instincts.
The anti-civilization motif
This novel features a false Adam and Eve story. Madelene even leaves a man whose name is literally Adam in order to become romantically involved with a smart ape. The point of all this is to highlight the anti-civilization sentiments of the novelist. We often believe that our roads, buildings, jobs, and markets make us different than the animals, but the purpose of this motif is to remind the reader that at a purely physical level, we're basically all just apes.
The alcohol motif
Alcoholism is the subject of many of the novel's scenes. Madelene is a serious alcoholic almost immediately upon her arrival to London. This is a symbol for the meaninglessness of Madelene's life. She drinks to forget the panic that sets in when she realizes that her life is not about anything real. She only fixes this problem when she is in nature, away from alcohol. The damage of alcohol in the story seems to represent itself. Alcoholism in this story is a sign for existential dilemma, not unlike real alcoholism in real life.
The DNA testing
The DNA testing on Erasmus is a plot device designed to help the reader contemplate what separates animals from mankind, if anything. Because Erasmus can speak, how different is he? Madelene finds that Erasmus's direct instincts and intuitions are way more healthy and meaningful than the pretense of modern civilization, and the DNA testing makes that all more direct and obvious.
