Is the Appendix a Vestigial Organ?

This is an abridged write-up on the role of the appendix written in part to answer Professor Dr. Andrew Charles Gomez, a very well-known ENT surgeon, whose question to me was, whether I agree with him that the appendix serves as a store house for beneficial bacteria, and has a role in nutrition.

I was asked for my opinion.

I fully concur with what Prof Gomez commented to questions asked in a round of mail exchanges circulated among friends, scientific and medical colleagues in a Whatsapp group.

EVOLUTIONARY BIOLOGY:

Here is my opinion  as an extension on evolutionary biology I recently studied, in that the appendix has evolved as part of a useful component of the gastrointestinal gut shown in several mammalian lineages, including probably in some of the earliest humanoids, the Neanderthals some 150 – 200 thousand years ago, and in the early homo sapiens according to anthropological and fossil records.

According to some more recent studies, this evolutionary linkage has persisted for thousands of years and has never disappears entirely. This suggests that the appendix may have served an adaptive purpose in gut physiology in all these mammalian species, including for modern humans for a very long evolutionary period in time.

Some previous studies on embryonic development, and into intrauterine life till about 1 -2 years post neonatal life in humans, as well as in many mammals, the appendix is statically-significantly larger by about 35 – 43 % than in adults.

EARLY INFANT NUTRITION:

This suggests that the appendix may play a very important role the early stages of early life support as part of the immunological defenses, as well as its role in paediatric nutrition when beneficial gut microbiota (gut bacteria) and pathogenic bacteria begin to establish themselves, often in competition with each other for their colonic habitat.

One purpose I hypothesize is that, in infant nutrition for the new born, milk sugar (lactose) in milk requires an enzyme (lactase) to breakdown for it to be bio-available to babies.

In adult humans who stop drinking milk post-weaning period, this enzyme may cease to produce, in that there would be no more epigenetic influence of the lactose in milk on specific genes that express the lactase needed to digest the milk sugars.

 As a clinical sequel in adult humans, especially among the Chinese and non-milk drinking Asians, they develop milk intolerance due to lactase deficiency as one of the reasons. There are also other genetic factors being considered.

 This role of lactase is then taken over by the gut bacteria such as lactobacilli to break down the milk sugar to make it available to infants (humans as well as babies of mammals).

Notwithstanding, milk intolerance in adults may be offset by the consumption of yogurt, fermented products and lactobacilli and the use of probiotics immediately following an ingestion of large quantity of cow’s milk for those who are lactose intolerant.

     

In infantile life, useful gut flora is supplied by the increased appendix size to total colon surface area ratio. There it serves as larger pouch and reservoir to shelter a larger populations of microbiota more effectively than what the rest of the colon’s ability.

It is the constant abrasive actions of the peristaltic contractions and motility of the intestines on colonic residues that constantly remove large population of gut flora, compared to the safe harbor of an inactive “vestigial” appendix.  

It has been my personal opinion on evolutionary biology, that it has been designed this way for the purpose of digestion of milk and the bio-availability other highly complex sugars and starches that would not have been possible in a highly motile colon.

GUT MICROBIOLOGY:

However, as the mammalian species (includes humans) grow, the microbiota too multiple proportionally, and they migrate towards the much larger surface area of the colon outside the appendix where space is not confined in a pouch, and where nutrients are limited. There outside the appendix the colonies of bacteria thrive best.

As a sequel, the appendix by natural design, atrophies into a vestigial part of the colon, serving as if it has no more physiological function.

As the milk-breaking as well as the complex starch breaking bacteria population shrinks and migrate from the now smaller appendix compared to the larger surface area of the large intestines, pathogenic bacteria gets into the appendix, and  occupy the vacant space where there is now lesser bacterial competition.

This is where and when opportunistic infections get hold, and where lymphoid tissue and antibodies are in decline, causing the notorious and common appendicitis.

It is unfortunate that bacteria multiply and spread into the much larger areas of the colon where food is aplenty and vacating an enclosed isolated appendix may not be the best evolutionary option for the individual.

One of the reasons for the migration is that, immune bodies in higher amounts are found in the appendix, but in lesser amounts in the lymphoid tissues of the colon and in the cecum.

Higher challenge by lymphoid tissues may not be adaptive for the beneficial gut flora. It is part of an adaptive response when environment becomes hostile.

This suggests that, that part of the vestigial colon has actually an immunological function since high concentration of lymphoid tissues is also found especially in the early stage of infantile development.

We know that the presence of lymphatic tissues and antibodies in the colon, cecum and appendix may promote the growth of beneficial microbiota and probiotic, such as Lactobacillus, Bifidobacterium which is extremely useful for colon health as well as in the synthesis of certain vitamins like folic acids.

In my opinion, combining what we already know in advances in gastrointestinal physiology, infant nutrition, gut microbiology, immunology and in evolutionary biology, I think the appendix has a well-deserved place in the biological evolution for  the well-being of colonic health, and thus cannot be labeled as a vestigial part of the colon as most scientists and medical experts think.

After all we have our own independent thinking, and we need to gather information from other areas of biomedical sciences as well and not just seen in one small corner of specialized medical or scientific discipline to resolve this age-old theory that the appendix is a vestigial organ with no physiological role. We need to think out of the box, and not be intellectually stagnant  

The only problem is when it gets infected by impacted food lodged there. That is when the classical appendicitis is presented, and needs to be surgically addressed.

But then we will also lose part of our developmental immunological system in that part of the anatomy which may initiate the risk of colorectal cancer? This is another area of interest 

I hope I have been of some help to your questions Prof Dr. Gomez.  But I do concur with your suggestion that the appendix has a role in gut nutrition.

Congratulations to you for your similar  thinking! 

Lim ju boo, Post-doctoral CE Cert. in Evol. Biol. (University of Cambridge)