How does Ernest in the novel Frankenstein support the theme of the book?
Ernest does not play a significant role in Frankenstein. In fact, most readers forget that he is the only surviving Frankenstein at the novel's end. Frankly, it seems that Mary Shelley had planned to do more with his character and then got sidetracked with other characters.
However, there are a couple of connections of Ernest to the novel's themes. In regards to Victor, Ernest serves as a foil character. Ernest, like Victor, grows up under the same permissive parents who stress compassion and Romantic qualities. However, he does not become obsessed with science or making a name for himself. In fact, he desires to join the military, but his father does not want him to. Ernest is also the opposite of Victor because he experiences the same deaths in the family as Victor does but does not become consumed by them. While it is true that Victor is responsible for many of the deaths in his family's, he gives up all logical thinking whenever anything happens, but Ernest seems to be there as a support for his father and Victor, calmly helping in whatever way he can. He accepts responsibility, while Victor does not.
Ernest's character also advances the idea that sometimes a lack of knowledge can be better for humans than too much knowledge. Ernest does not know what truly happened to many of his family members, but he also does not struggle as his brother does. Victor knows too much about the crimes committed against his family and friends and eventually becomes obsessed with seeking revenge.
It is interesting that readers know so much about Victor by the novel's end but do not even know what Ernest's fate is. Perhaps Shelley forgot him.