THE APPENDIX IS A MICROBIOME REFUGE.

THE APPENDIX IS A MICROBIOME REFUGE:

The appendix has long been considered a vestigial organ, its function lost as we climbed to the top of the evolutionary ladder. It’s also considered a troublesome nuisance, causing a quarter of a million cases of appendicitis in the US every five years, and 72,000 deaths every year world-wide.

Given this human cost, why do we still have an appendix? Why hasn’t evolution driven it to extinction?

It turns out the there’s a very good, adaptive reason why we still have an appendix. The appendix is a safe-house in the lower gut where “friendly” bacteria can seek refuge in the face of a serious pathogenic onslaught – and from which they can emerge once the carnage is over to re-populate the gut with a benign microbiome.

A recent paper in Comptes Rendus Palevol titled “Morphological evolution of the mammalian cecum and cecal appendix” reveals that the appendix has evolved a minimum of 29 times, possibly as many as 41 times, throughout mammalian evolution, while it has only been lost a maximum of 12 times. This is strong evidence that the appendix is a structure selected for in evolution.

The study specifically found that ecological factors that affect the incidence of gastrointestinal infection had influenced the evolution of the appendix. So, the appendix, which is richly-endowed with lymphoid tissue, they argue, may have evolved as an adaptive immune response to pathogen avoidance as well as a refuge for benign microbes.

Read the entire article here: https://www.researchgate.net/publication/258559329_Multiple_independent_appearances_of_the_cecal_appendix_in_mammalian_evolution_and_an_investigation_of_related_ecological_and_anatomical_factors?ev=srch_pub