Three thousand years before the story starts, Lysos founds a human colony on the isolated planet of Stratos in an effort to radically re-engineer human life into a happier, more pastoral form. She developed a strain of human beings that conceives clones in winter (always female), while those conceived in summer (variants or "vars") obtain their genes through sexual reproduction just in case biological adaptation becomes necessary. Further, males and females have opposed seasons of sexual receptivity: men in summer and women in winter. This scheme is said to be stable over evolutionary time because women gain an advantage from self-cloning, while men only reproduce in summer. Finally, men have been made far less aggressive during the times that they are less sexually receptive and are much less numerous. The social result is that the vast majority of the population of Stratos consists of groups of female clones, each in its own social or economic niche. Over the centuries, these groups have come to dominate society. Men are confined to relatively few professions (such as sailing) and have a lower social status than clones, but higher than vars. In each generation, a few women vars become successful enough to found their own clan or "hive" of clones.