Figs. 2ei–ii, 1f (series):
In other instances, the link between Lovecraft’s race thinking and his fiction was more implicit. As we have seen in sections one and two, one of Lovecraft’s main sources of existential dread was miscegenation. One aspect of this is a fear and hate toward the racial Other, as we have seen with “The Horror at Red Hook.” Another aspect, however, is a sort of inward fear toward the unknowability of one’s ancestry. What if one is part of “the wholesale pollution of highly evolved blood by definitely inferior strains” (fig. 2ei–ii)?
Literary scholar Mitch Frye calls this trope “genotypic horror,” a “storytelling mode that exploits genetic fear.” This type of story “shows the individual at war with a cold, chaotic world as well as with the mysterious machinations of his own genes,” which “might reveal some dark inherited element of his family’s past” The source of horror is the latent character of one’s “inferior blood”; it is a haunting that passes down for generations. Indeed, it is the “pollution” of a whole family tree by its “loftier branches” (fig. 1f).
Two examples of genotypic horror are the stories “Facts Concerning the Late Arthur Jermyn & His Family” (figs. 4a and 4c) and “The Shadow over Innsmouth” (figs. 4b and 4d). Both stories have similar plots: they follow an intellectually inclined young white male from a family with a “troubled” history interested in his family’s genealogy, only to discover that he has a racialized Other female ancestor. This leads to an existential crisis that completely upends the protagonist’s life.
Fig. 4c (series):

In “Arthur Jermyn,” the eponymous protagonist takes an interest in the anthropological pursuits “in the Congo region” by his great-great-great grandfather Sir Wade Jermyn (fig. 4ci). There, Sir Wade married the mysterious “daughter of a Portuguese trader” (fig. 4ci), who is later revealed to be a “white ape of some unknown species” (fig. 4ciii). When Arthur discovers that his great-great-great-grandmother is someone who was between “human or simian” (fig. 4ciii), he loses his mind and commits suicide by self-immolation.

Fig. 4d (series):

Whereas “Arthur Jermyn” primarily focuses on the “personal” tragedy of the Jermyn family, “The Shadow Over Innsmouth” combines genotypic horror with Lovecraft’s larger fears of the dilution of the Anglo-Saxon “cultural stream” in the United States. The story follows Robert Olmstead, who is taking a trip across New England to learn more about his ancestry (recall Lovecraft’s own “ancestral pilgrimages”). In this trip, he stumbles upon the dilapidated town of Innsmouth, which is severely disliked by neighboring towns. Olmstead later finds that the Innsmouth residents are in a sort of symbiotic relationship with a race of fish-like humanoid amphibians named “the Deep Ones,” which inhabit a nearby reef. The Deep Ones provide plenty of fish and sometimes jewelry (i.e., economic security) to Innsmouth in exchange for worship. Furthermore, Innsmouth’s residents procreate with the Deep Ones, to the extent that most of the town’s inhabitants are a human-Deep One mix and have a human appearance, but they change into Deep Ones once they reach middle age, forcing them to move to underwater cities. Even more troubling is Olmstead’s discovery that the Deep Ones plan to “expand” to other places beyond Innsmouth. At the end of the story, Olmstead realizes he is the descendant of the Deep Ones and readies to leave for their underwater cities.