In “Ayako,” Osamu Tezuka draws on that offshoot of literary realism called Naturalism. Emile Zola and others working in that tradition were greatly influenced by Charles Darwin, though their understanding of his theory was idiosyncratic, and they put it to their own uses. Mostly what they took from Darwin’s work was the notion that we are all prisoners of our heredity (a notion that wasn’t exactly new: novelists had been using “blood” to explain their characters for a long time) and our social environment. “Prisoners” is the key word here: one’s heredity and circumstances seldom, in the Naturalists’ view, left one free to live a happy, healthy life: They were more likely to compel one toward vice, poverty, crime, incest and alcoholism.