 This episode and part two "The Family of Blood" were adapted by  scriptwriter Cornell from his 1995 Doctor Who novel, "Human Nature".  This marks the first time in Doctor Who history that a novel based  upon the series was adapted as an episode. Many changes were made in  transferring the novel to the screen. The original book featured the  Seventh Doctor and his companion, Benny Sommerfield, and the  Doctors motive for becoming human was to study the human condition,  not to flee aliens.