Complex sentence: Andro is one of the few remaining survivors of a biological disaster brought on by an ambitious scientist named Bertram Cabot, Jr., who had isolated and developed a viral symbiont from an interstellar microbe which physically altered the human race, precluding the ability to reproduce.
Split into simpler sentences: Andro is one of the few remaining survivors of a biological disaster brought on by an ambitious scientist named Bertram Cabot, Jr., who isolated and developed a viral symbiont from an interstellar microbe. Cabot's symbiont physically altered the human race, precluding the ability to reproduce.