The vermiform appendix is a vestige of the cecum , an organ that would have been used to digest cellulose by humans’ herbivorous ancestors. One potential ancestral purpose put forth by Charles Darwin was that the appendix was used for digesting leaves as primates. It may be a vestigial organ, evolutionary baggage, of ancient humans that has degraded down to nearly nothing over the course of evolution. Evidence can be seen in herbivorous animals such as the koala. The cecum of the koala is very long, enabling it to host bacteria specific for cellulose breakdown. Human ancestors may have also relied upon this system and lived on a diet rich in foliage. As people began to eat more easily digested foods, they became less reliant on cellulose-rich plants for energy. The cecum became less necessary for digestion and mutations that previously had been deleterious were no longer selected against. These alleles became more frequent and the cecum continued to shrink. After thousands of years, the once-necessary cecum has degraded to what we see today, with the appendix. Analogous organs in other animals similar to humans continue to perform that function, whereas other meat-eating animals may have similarly diminished appendices. In line with the possibility of vestigial organs developing new functions, some research suggests that the appendix may guard against the loss of symbiotic bacteria that aid in digestion. An alternative explanation would be the possibility that natural selection selects for larger appendices because smaller and thinner appendices would be more susceptible to inflammation and disease.