Important biological function of an Appendix Discovered

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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

Researchers from the Midwestern University Arizona College of Osteopathic Medicine have worked on a study that one theory suggests it could serve as “a reservoir” for beneficial gut bacteria.

The researchers’ findings suggest that it plays a part in our immunity, calling it a "microbial safe-house for beneficial bacteria". 

First they gathered data on the presence or absence of the appendix and other gastrointestinal and environmental traits across 533 mammal species over the past 11,244 million years.

Onto each genetic tree for these various lineages, they traced how the appendix evolved through years of evolution, and found that once the organ appeared, it was almost never lost.

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

Next, the researchers considered various ecological factors - the species' social behaviours, diet, habitat, and local climate - to figure out what that "adaptive purpose" could be.

They found that species that had retained or regained an appendix had higher average concentrations of lymphoid (immune) tissue in the cecum - a small pouch connected to the junction of the small and large intestines.

This suggests that the appendix could play an important role in a species' immune system, particularly as lymphatic tissue is known to stimulate the growth of certain types of beneficial gut bacteria.

"While these links between the appendix and cecal factors have been suggested before, this is the first time they have been statistically validated," the team concludes in their paper.

"The association between appendix presence and lymphoid tissue provides support for the immune hypothesis of appendix evolution."

The study is far from conclusive, but offers a different perspective on the hypothesis that humans have been keeping the appendix around for its immune support this whole time.

The challenge now is to prove it, which is easier said than done, seeing as most people who have had their appendix removed don't suffer from any adverse long-term effects.

But it could be that when people get their appendix removed, immune cell-producing tissues in the cecum and elsewhere in the body step up to compensate for the loss.

One thing's for sure in all of this - while we're probably not going to regain our tails, it's too soon to write off the appendix just yet.

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