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|Arteries of cecum and vermiform appendix. (Appendix visible at lower right, labeled as "vermiform process").|
|Normal location of the appendix relative to other organs of the digestive system (frontal view).|
|Gray's||subject #249 1178|
The caecum is a pouch-like part of the colon. The appendix is near the junction of the small intestine and the large intestine. The term "vermiform" comes from Latin and means "worm-like in appearance".
Darwin suggested that the appendix was perhaps used to digest leaves as primates. Over time, humans have eaten fewer vegetables and have evolved. Over thousands of years, this organ has become smaller to make room for the stomach. It is a vestigial organ which has degraded to nearly nothing in the course of evolution.
Herbivorous mammals such as the Koala have large appendices, and usually other adaptations as well. Cellulose, from plant cell walls, is hard to break down. The cecum of the koala is attached to the juncture of the small and large intestines as it is in humans, but is very long. This enables it to host bacteria specific for cellulose breakdown.
Early man’s ancestor may have also relied upon this system and lived on a diet rich in foliage. As man began to eat foods easier to digest, 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; the appendix. 
Evolutionary theorists have suggested that natural selection selects for larger appendices because smaller and thinner appendices would be more susceptible to inflammation and disease.
- Darwin, Charles 1871. The Descent of Man, and selection in relation to sex. John Murray: London.
- "The old curiosity shop". New Scientist. 2008-05-17. http://www.newscientist.com/channel/being-human/mg19826562.100-vestigial-organs-remnants-of-evolution.html.