“Big Ancestor,” F. L. Wallace, 1954 — In a quest to find the ancient race that seeded the galaxy with humanoid life, human beings discover that they were once the pests of the universe. Their prevalence in the universe is not due to an inherent superiority but to their talent for infesting alien ships.
Comments: Read in Five-Odd.
Author: Wikipedia: “F. L. Wallace, sometimes credited as Floyd Wallace, was a noted science fiction and mystery writer.”