From the Sci-Fi Wire:
Alfonso Cuaron, director of the upcoming SF drama Children of Men, told SCI FI Wire that he loved the stylistic world in the novel by British mystery writer P.D. James on which the movie is based. But he added that he wanted to depart from the science-fiction aspects from the start. “I loved the world she created in the book, but it was not something I could see myself doing,” Cuaron said. “I used the book as a jumping-off point.”
Having been disappointed, ultimately, in James’ original novel, I don’t really have a problem with these changes. (The decision to make it the women who are infertile instead of the men, on the other hand…)
I just hope the film can improve on the novel, which I thought established a really frightening and plausible vision of the future — only to waste it on what was essentially one long chase scene. The trailer for the film, I thought, looked interesting, but we’ll see.