The town of Eyam in central England is often referred to as the 'plague village.' In the summer of 1665, an outbreak of the plague was discovered in the town, and the residents decided to isolate themselves to prevent the spread of the disease. After nearly a year and a half, when they reopened to outsiders, it was found that over 70% of the population had perished. Interestingly, about 30% of the population survived. Some families lost all but one member: for instance, John Smith lost his wife and three children but never contracted the plague himself. Smith's case was not isolated; many survivors appeared to be immune to the infection. Researchers have noted that a significant number of descendants of plague survivors from Eyam carry a mutation of a gene known as delta 32.

Which of the following, if true, most undermines the implications made within the passage?