• The article traces two phases of SF about human species change, the first in the 1940s and early 1950s, the so called “golden age” of SF. In this first phase the advent of the posthuman is brought on by eugenics or sudden mutations caused by fallout from nuclear war. It consists of well-known books by most of the leading authors of the period: Clarke’s Childhood’s End, Sturgeon’s More Than Human, Van Vogt’s Slan, Heinlein’s Beyond This Horizon and Methuselah’s Children, and a number of lesser known texts. The second phase got under way in the late-1970s and lasted up until just before the millennium. Stimulated by excitement over recombinant DNA and the first test-tube baby in 1978, the surge of interest in genetic transformations of the human explored genetic engineering rather than evolution as the source of the posthuman. The fiction considered includes Octavia Butler’s The Xenogenesis Trilogy, Greg Bear’s Darwin’s Radio and its sequel, Bruce Sterling’s Schismatrix. The article concludes with a look at a third group of books, nonfiction about the posthuman by bioethicists and policy experts published since 2002. I characterize this last body of work as either variants of the American jeremiad Sacvan Bercovitch described or as “anticipations” in the optative mode of popular science writing pioneered by H. G. Wells in his book by that name, Anticipations (1901). Throughout the article, I emphasize the covert relationship between nonfiction policy works—for and against genetic enhancement—to what Istvan Cscicsery-Ronay called “science-fictional habits of mind . . .a mode of response that frames and tests experiences as if they were aspects of a work of science fiction.”