Embryo adoptions, stem cells capable of transforming into any cell in the human body, intra- and inter-species organ transplantation - these and other biomedical advances have unsettled ideas of what it means to be human, of growth and aging, of when life begins and ends. Susan Squier argues that fiction - particularly science fiction - serves as a space where worries about ethically and socially charged scientific procedures are worked through; in many instances science fiction anticipates and paves the way for biomedical changes. Squier uses the anthropological concept of liminality - of physical entities or moments of time on threshold of change, not quite one thing but not yet another - to explore how, from the early twentieth century forward, fiction and science together have altered the concept of the human being. Squier explains her methodology for highlighting the connections between literature and science by providing brief histories of the development of two fields - literary criticism and feminist science studies. Drawing on archival materials of twentieth-century biology and little-known works of science fiction, she examines a number of biomedical changes as each was portrayed by scientists, social scientists, and authors of fiction and poetry. Among the scientific developments she considers are the cultured cell, the hybrid embryo, the engineered intrauterine foetus, organ transplants, and the artificially rejuvenated elderly person. Squier shows that in the midst of new entities such as these, literature plays a crucial role: It helps us explore the implications of the newly engineered human lifespan for our relations with each other, with other species, and with the earth. It allows us to reflect on the plots, possibilities, and perils of our liminal lives.