"Big Ancestor" by F. L. Wallace is a science fiction novel published in the early 1950s. The narrative explores themes of evolution, interstellar travel, and the origins of humanity as it follows an expedition team searching for their ancestral roots within the Milky Way. The characters include both humans of different evolutionary stages and an alien pilot known as Taphetta, offering a unique perspective on human interbreeding and the biological spectrum of the species. The storyline revolves around a group of researchers and scientists led by Sam Halden, who embarks on a journey through space to uncover the truth about human origin and their connection to an ancient, long-forgotten civilization. As the crew encounters various species, they grapple with their racial identities and the implications of their shared lineage. They eventually discover a deserted planet of a once-advanced civilization that had previously fled due to an uncontrollable plague, which ironically, had mutated from vermin they unwittingly allowed aboard their ships. This twist not only challenges the characters' perceptions of superiority and progress but leaves them facing a disconcerting truth about their own history. (This is an automatically generated summary.)