John Michael Crichton was an American author, screenwriter and filmmaker. His books have sold over 200 million copies worldwide, and over a dozen have been adapted into films. His literary works heavily feature technology and are usually within the science fiction, techno-thriller, and medical fiction genres. Crichton's novels often explore human technological advancement and attempted dominance over nature, both with frequently catastrophic results; many of his works are cautionary tales, especially regarding themes of biotechnology. Several of his stories center specifically around themes of genetic modification, hybridization, paleontology and/or zoology. Many feature medical or scientific underpinnings, reflective of his own medical training and scientific background.