As a biologist I know that human children that are raised together are averse to having sex with each other because of a complex network of genes that have evolved in order to prevent these sorts of relationships from yielding offspring. The offspring of closely related family members typically inherit all the recessive or abnormal genetic traits. In the Anthology’s introduction to Tis Pity She’s a Whore by John Ford (not assigned reading), the authors discuss the theme of incest. They tell us that dramatists stage incest because it is a matter that the audience pays serious attention to. Most times incest is associated with the villains. In the The Duchess of Malfi, incest was not discussed directly, but rather through Ferdinand’s obsession with his sister’s sex life. Ferdinand’s suppressed sexual desire of his sister morphed into a desire to see her dead. From incest to sororicide, the descent is quite rapid and as a member of the audience, I am riveted. I look forward to seeing how “Ford makes the incestuous lovers central and… rather ordinary” (p1905) in Tis Pity.
ASIDE: I also recommend A Song Of Ice and Fire by George RR Martin and the spin off Game of Throne on HBO for the dramatization of incest and sororicide on Middle Earth (which is strangely like Renaissance England).
The institutional corruption depicted in ‘Tis Pity is so great that Giovanni and Annabella, the brother and sister, seem less depraved than they might otherwise look. They are assisted by her maid, Putana, whose name bespeaks her indifference to the taboos that are being broken.