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 mapped the data onto a phylogeny (genetic tree) to track how the appendix has evolved through mammalian evolution, and to try to determine why some species have an appendix while others don’t.
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. Paper. (paywall) – Heather F. Smith, William Parker, Sanet H. Kotzé, Michel Laurin. Morphological evolution of the mammalian cecum and cecal appendix. Comptes Rendus Palevol, 2017; 16 (1): 39 DOI: 10.1016/j.crpv.2016.06.001 More.
The principal function of the appendix in recent decades has been to provide Darwinian propagandists with an easy example of a “vestigial” organ to point to—a function somewhat like that of “junk DNA/RNA.” When a given claim is shown not to be true, no fear, they just cease being polite and camp on the next apparent example. There are many life forms to choose from so they can go on inhibiting fresh approaches until they retire.
If an organ that is not used by current life forms within a lineage tends to persist, might it be conserved as part of a package that can be repurposed later? That, of course, assumes a non-Darwinian approach to evolution, so the enquiring mind had better enquire about something else at present.
See also: Appendix has a use after all? Has recently retired from being “vestige of evolution” …
Appendix not even redundant, let alone vestigial?
See also: Appendix, no “vestigial organ,” is a safe house for useful bacteria, researcher says
They knew the human appendix did a job sixty years ago, actually
Your appendix: The king of vestigial organs has a job again
“Junk” RNA helps regulate metabolism
Junk DNA defender just isn’t doing politeness any more.
Anyone remember ENCODE? Not much junk DNA? Still not much. (Paper is open access.)
Yes, Darwin’s followers did use junk DNA as an argument for their position.
Another response to Darwin’s followers’ attack on the “not-much-junk-DNA” ENCODE findings
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