John Glasby & John C. Maxwell 
World Makers [EPUB ebook] 

Earth had been destroyed, but man had built his colonies on Mars and Venus and the far-flung moons of Jupiter and Saturn. Mutation and forced breeding had changed these people so they were no longer human. Clyde Lester, the last man on Earth, had a special problem. From somewhere in space there originated strange radio signals which could only come from beyond the orbit of Pluto, the outermost planet.