We have been believing for more than a century that the appendix is ​​a useless organ and an evolutionary error. We were very wrong

If there is an organ with a bad reputation in human anatomy, it is the appendix. For the vast majority of people, this small worm-shaped pouch connected to the large intestine only serves one thing: to become inflamed, to cause appendicitis urgently and have us undergo surgery. But the truth is that it is more useful than we thought, since science has seen that it has a great impact on our immune system and also in life expectancy.

An evolutionary success. Something that marvels me about evolution is that it does eliminate everything that has no use for humans, but if the phylogenetic branch has been maintaining it, it is for a reason. and here a 2013 study analyzed the anatomy of 361 species of mammals and the results were devastating: the appendix is ​​not exclusive to humans and great apes, but has evolved independently at least 32 times. And the question is: why?

This theory was later reinforced with a 2017 analysis which identified between 29 and 41 evolutionary gains of the appendix, compared to the very few losses that stood at less than seven. And in biology, when a trait evolves repeatedly in completely different lineages, it means one thing: it provides a crucial adaptive advantage for survival.

Its usefulness. If it doesn’t help digest leaves as Darwin believed, then… What does it do? The latest research, including a comprehensive 2023 review published in The Anatomical Record, confirm that the appendix acts as a microbial reservoir and a support for the immune system.

This way we know that the appendix is ​​filled with lymphoid tissue and is strategically located outside the “main flow” of the intestine. And it works as a kind of bunker for our microbiome, and in this way, when we suffer a severe intestinal infection that “sweeps away” our bacterial flora, the appendix releases beneficial bacteria hidden inside to quickly recolonize the intestine.

And tested. A 2023 study showed that primates with appendages have a relatively lower risk of severe diarrhea episodes early in life, reinforcing their vital role as a protective shield against deadly infections.

Its relationship with longevity. The most fascinating discovery about the appendix came in 2021, where a team of researchers published in the journal Ecology and Evolution a study in which they crossed data from 258 mammal species. Controlling for variables such as body size and phylogeny, they looked for patterns between the presence of an appendage and the lifespan of the species.

The conclusion they drew was none other than determining that the presence of the appendix is ​​directly correlated with greater maximum longevity. And the reason is in positive natural selection. In this way, by drastically reducing mortality caused by infectious diseases and diarrhea, species with an appendix have a clear survival advantage that allows them to extend their life expectancy.

Image | Eugene Chystiakov

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