No Spare Parts
For much of human's history of biological knowledge, the appendix has been considered an organ without a purpose. If you Google, "Appendix Function", the first explanation is, "The function of the appendix is unknown." It is deemed a vestigial structure. There are, however, numerous theories.
One theory, that actually fits testing, is that the appendix is an incubator for gut bacteria, or gut flora, specifically for breaking down plant based foods ("good bacteria"). Further evidence is that the only animals that possess an appendix are herbivores. The theory then assumes that early human ancestors, along with chimpanzees, gorillas, etc., were herbivores, but the human's appendix function was lost as they evolved to eat meat leaving the appendix a useless relic. From the scientific data, however along with personal experience, I have a different perspective: humans are still anatomical herbivores with a still functional appendix, but most people's appendix simply suffers a bad case of atrophy. The data does show this, however, it is traditionally interpreted through a carnism filter.
During a meal at a family gathering, it was pointed out, to me, that humans cannot digest corn. Apparently, this was in response to the large serving of whole kernel corn on my plate. It was pointed out that corn exits the body, intact, just as it was when eaten. I eat a large serving of whole kernel corn every day and I never see any evidence of those kernels again. I believe this is because my appendix is working and I have a healthy cellulose digesting gut flora. With this curiosity, I have asked other whole food plant based vegans if they ever see whole kernel corn exit, and their answer is that they do not.
This leads me to conclude that just like any other body part, the appendix is subject to atrophy if never or insufficiently used. Eating meat introduces a very different gut flora which is not compliant with the human appendix function, thus atrophy sets in, leaving the medical, and scientific community to conclude that it has no anatomical purpose.
Please understand that I am not a medical professional in any capacity. This writing is only to share my experience and what I have learned from it.
Nothing in life is more inhibiting, failing or debilitating than the belief; "I Can't."
Nothing in life is more freeing, enabling or successful than the belief; "I Can."