More research supporting that the appendix has a purpose - that it has an immune function and is a "reservoir" for beneficial gut bacteria. That is, it is where beneficial bacteria go and hide out when the person has food poisoning or is taking antibiotics (which wipe out bacteria in the gut), and then these bacteria replenish the gut afterwards. (Other supporting research.) This is the opposite of what many have believed for years (and we were taught in school) - which was that it is something that may have had a purpose long ago, but now is a "vestigial organ" and useless in humans. Hah! Once again scientific knowledge is being rewritten.
The researchers examined 533 mammal species for the presence of an appendix, and found it in a number of them, including humans, chimps, and dogs. From Science Daily:
The human appendix, a narrow pouch that projects off the cecum in the digestive system, has a notorious reputation for its tendency to become inflamed (appendicitis), often resulting in surgical removal. Although it is widely viewed as a vestigial organ with little known function, recent research suggests that the appendix may serve an important purpose. In particular, it may serve as a reservoir for beneficial gut bacteria. Several other mammal species also have an appendix, and studying how it evolved and functions in these species may shed light on this mysterious organ in humans.
Heather F. Smith, Ph.D., Associate Professor, Midwestern University Arizona College of Osteopathic Medicine, is currently studying the evolution of the appendix across mammals. Dr. Smith's international research team gathered data on the presence or absence of the appendix and other gastrointestinal and environmental traits for 533 mammal species.
They discovered that the appendix has evolved independently in several mammal lineages, over 30 separate times, and almost never disappears from a lineage once it has appeared. This suggests that the appendix likely serves an adaptive purpose. Looking at ecological factors, such as diet, climate, how social a species is, and where it lives, they were able to reject several previously proposed hypotheses that have attempted to link the appendix to dietary or environmental factors. Instead, they found that species with an appendix have higher average concentrations of lymphoid (immune) tissue in the cecum. This finding suggests that the appendix may play an important role as a secondary immune organ. Lymphatic tissue can also stimulate growth of some types of beneficial gut bacteria, providing further evidence that the appendix may serve as a "safe house" for helpful gut bacteria.
Drawing of colon seen from front (the appendix is colored red). From Wikipedia