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The appendix often goes unnoticed until it causes a problem that requires removal. Wouldn't it be better if we had never had an appendix? Darwin once suggested that the appendix didn’t serve any distinct purpose and was simply a remnant of a much larger cecum that shrank into a small, unnecessary fold.
However, Darwin didn't have the full story. New findings from Dr. William Parker at Duke University and other researchers indicate that not only was the appendix once crucial, it continues to play an important role in certain regions of the world. It turns out the appendix is not a vestigial organ after all.
In 2007, Dr. Parker and his team of immunologists at Duke University published a study suggesting that the appendix functions as a 'safe house' for helpful gut bacteria during serious gastrointestinal illnesses. After the immune system has fought off the disease, the healthy bacteria stored in the appendix rapidly replenish the gut microbiome.
"[The appendix] seems to be perfectly positioned to reboot the body in case of an infectious illness—like cholera or typhoid, or any other gut infection that triggers a diarrheal response," Dr. Parker tells mental_floss.
In 2013, Dr. Parker collaborated with a global team of researchers to trace the evolutionary history of the appendix. Their study examined the diets of 361 living mammals and revealed that the 50 species now known to possess an appendix are spread so widely across the mammalian evolutionary tree that the appendix must have evolved independently at least 32 times, and possibly up to 38 times.
"It’s a recurrent trait—it appears and disappears but only in specific mammal groups, while in others, it’s completely absent," Parker explains. This idea supports Dr. Parker's safe house theory. In most cases, when the appendix first appears in a species, there is no dietary change, contrary to Darwin’s belief that it would occur alongside a shrinking cecum. Evolution repeatedly selected for the appendix, likely due to its immune system-supporting function.
But does it still help protect beneficial bacteria? "We think so, that's the hypothesis. Of course, no one is willing to conduct that experiment," Dr. Parker said.
In developed nations, "[the appendix] was probably quite useful around 1850, perhaps even as late as 1890. However, since around 1950, when toilets became widespread in the U.S., its usefulness has greatly diminished." It likely remains crucial in developing countries where gut infections are still common.
The appendix's potential role in supporting the immune system suggests that, contrary to common belief and its classification as a useless organ, it may not actually be vestigial. As Dr. Parker puts it, "We’ve had some social changes that have made a lot of parts of our immune system inactive."
