“Once Clem Pre-Mammal was done filling his stomach and squirting his sperm around, sleep kept him immobile and away from predators. Sleep was an aid to survival. But now it's a left-over mechanism, a vestige like the appendix. It switches on every night, but the need is gone.” 

While some researchers believe that sleep also allows humans to forge new neural pathways and preserve memories, there is little empirical evidence to support these theories. This lends credence to Susan's assertion above that sleep is a vestigial mechanism. As the book progresses, however, it becomes clear the author believes there are immense creative and intellectual benefits to dreaming that the Sleepless cannot enjoy.

“See, Leisha—this tree made this flower. Because it can. Only this tree can make this kind of wonderful flower. That plant hanging up there can't, and those can't either. Only this tree. Therefore the most important thing in the world for this tree to do is grow this flower. The flower is the tree's individuality—that means just it, and nothing else—made manifest. Nothing else matters.” 

Roger explains to his daughter the importance of individuality and being true to one's self, two ideas that will be of immense importance to Leisha both personally and politically. In addition, it introduces plants and flowers as symbols of individuality, symbols that will re-emerge particularly as they relate to Leisha's relationship with Alice. For example, Alice insists on sending Leisha common flowers rather than exotic ones, as if to remind her that Sleepers are individuals too.

“No, the only dignity, the only spirituality, rests on what a man can achieve with his own efforts. To rob a man of the chance to achieve, and to trade what he achieves with others, is to rob him of his spiritual dignity as a man.” 

This is the earliest and most direct distillation of the Yagaiism philosophy to which Leisha and others adhere for much of the book. Yagaiism shares several similarities with Objectivism, a philosophy developed by the Russian-American author Ayn Rand. Rand endorses a laissez faire system of capitalism in which men and women owe nothing to each other outside of voluntarily agreed upon contracts.