John Wyndham considered this story a study in "realism in interplanetary travel." This is no ordinary interplanetary story: it is a human and gripping adventure of explorations into a new world with a surprising series of developments.

What Mr. Harris shows so powerfully is the effect of environment upon two races: the rise of one and the steady degeneration of another to almost the level of the brute. As he points out, when men from temperate climates have gone to the tropics, one of two things has happened: they have either transformed the tropics and tamed it to civilization or else the tropics have conquered them and they have sunk slowly to the level of nature. The same struggle must go on when men go to other worlds to live and colonize.