Given Ralph's hatred of Smike and Nicholas both, it is deeply ironic that Smike ends up being Ralph's biological child. This use of irony may appear quite surface-level to readers—a mere plot device, intended to provide intrigue and keep readers hooked as the story progresses. Given Dickens's social-scientific context at the time of Nicholas Nickleby's publication, however, the implications of this plot point run deeper.
Ralph and Smike are two remarkably different people. Smike is kind, trustworthy, and loyal, looking up to Nicholas as a friend and guiding figure. Ralph is horrible, cruel, and vindictive, intent only on completing those tasks that satisfy his own ends. This difference between parent and child flies directly in the face of Social Darwinism, a philosophy that arose over the course of the mid-19th century. Many Social Darwinists held that personality traits (vices included) could be passed from parent to child, and that if children turned out to be alcoholics, or sexual "deviants," or criminals, the parents were to blame for "passing" those traits down to their offspring. Nicholas Nickleby breaks from this philosophy, showing that Smike "inherits" nothing of his father's moral bankruptcy, choosing to be a good person despite his environment and parentage.