This paper observes the aspects of human-alien relationship in Octavia E. Butler's Lilith's Brood trilogy (Dawn, Adulthood Rites, Imago). My thesis focuses on Butler's social criticism and the judgement of human nature represented through the linkage between Oankali and humanity. The three chapters discusses the main levels of the interspecies liasion - the human interpretation of Oankali behavior, the Oankali treatment and analysis of human mentality and the mutual bond developed between humankind and the alien species. By observing the multi-layered relations between the two species, this paper discusses Butler's criticism related to human nature and society.