The river in the novel is used to divide the advanced ape-men from the less advanced one. The river serves almost as a barrier between the two tribes and it protects them from one another. Thus, the river in this case, is used to symbolize the idea that not everyone develops in the same way. As it was clear in the time of the ape-men, not every one of them became smart and began to figure things out on their own. In fact, the number of prehistoric humans that managed to advance was relatively low.
The stone that suddenly appeared marked the beginning of a new era and served as a catalyst that started the development of humankind. Thus, the stone appears here as a symbol that marked the birth of the world as we know it today. From that point on, people continued to grow until they reached the lever of technology described as existing around the year 2000.
While men changed, women did not. The woman’s place in society remains the same and rather than being seen as humans capable of accomplishments, women are seen as entertainment for men. They are linked with man’s primitive desires and thus seen as being inferior. This idea is maintained throughout the novel and can be considered as being a motif.
Robots and humans
Robots and other technological units are treated as human in the novel. When Hal begins to malfunction, the crew members treat the robot as they would treat a human and it is implied that the robot feels human as well and that it feels ashamed that it is malfunctioning. The idea that robots are almost humans is a recurrent motif in the novel.
Hal is in the novel the supercomputer that helps the human crew gets to Saturn. At one point however, Hal begins to malfunction and puts everyone’s life in danger. In the novel, Hal is more than just a character; it is also a symbol that represents technological advancement. But Hal cannot be controlled and so he also represents the danger advanced technology imposes on the human race.