Beggars in Spain, like many works of science fiction, is primarily a novel of ideas. The difficulties and dilemmas of individuals generally lead to a consideration of wider concerns of humanity.
Leisha Camden's Sleeplessness and the benefits to which it gives rise provide a case in point. As human beings are increasingly able to modify themselves, to what extent should they do so, and what problems might this cause? Leisha does not choose her Sleepless status, but her father regards it as an unalloyed benefit. Sleep, he believes, is a waste of time, and being Sleepless also raises one's IQ and makes one happier. After his death, Leisha discovers that Sleeplessness also halts the ageing process. The Sleepless will live for much longer than those who have to sleep, and may even be immortal.
The problems faced by Leisha and the other Sleepless characters, however, raise issues even wider than genetic modification. They represent all the challenges posed by social inequality. When Leisha finds that there are other Sleepless people, they quickly form an aristocracy of high-achievers who are the target of resentment and violence from those less fortunate. Leisha has to navigate between the malice of some of the Sleepers, and the elitism of a faction of the Sleepless, who want to break off into a separate community with no Sleepers in it. This raises no less a concern than how people are to live together in an unequal society, particularly when the inequalities are continually exacerbated by technology.