In his previous science-fiction novel, Last and First Men, Olaf Stapledon envisioned 2 billion years of history, in which modern humans represented the first and most primitive of 18 increasingly advanced species. In this companion piece, a being from the remote future travels back to the 20th century to inhabit the consciousness of an Englishman named Paul. From inside his subject's mind, the superintelligent mega-human observes Paul's childhood,...