Question

For generations, the human appendix was widely regarded by physicians and evolutionary biologists as a vestigial organ—a useless remnant of our evolutionary past. Charles Darwin himself posited that the appendix was a shrunken trace of a cecum, an organ used by our herbivorous ancestors to digest tough cellulose. Because people can live healthy lives without it, and because it is prone to life-threatening inflammation (appendicitis), modern medicine historically treated it as a design flaw.

However, recent research in immunology and microbiology has challenged this long-held assumption. Scientists now propose that the appendix serves as a crucial "safe house" for beneficial gut bacteria. During severe digestive illnesses, such as cholera or dysentery, helpful bacteria are often flushed out of the intestines. The appendix, with its narrow opening and location at the beginning of the large intestine, remains protected from the path of infection. Once the illness passes, the bacteria stored in this immunological sanctuary emerge to repopulate and restore the gut microbiome. This protective function is especially vital in regions lacking modern sanitation, where diarrheal diseases are common. Thus, rather than an evolutionary mistake, the appendix appears to be a specialized adaptation designed to preserve digestive health.

Which of the following best describes the primary purpose of the passage?