One organ labeled as vestigial is the appendix. All my life, I have heard that it serves no useful purpose. Even if there is no immediate danger to a patient, doctors will often remove an appendix. However, it appears that the appendix has a use after all. Here is a section of an article from Mental Floss:
“Our study was to investigate the innate lymphoid cells in the gut [of mice] and how they might contribute to the function and protection of the gut,” Gabrielle Belz, of Melbourne’s Walter and Eliza Hall Institute of Medical Research, tells mental_floss. “At the same time, we were interested to know how different immune cells impacted the different parts of the gut.
"ILCs can be found “underlying all the body’s surfaces, including the skin, the lungs, the gut, and the reproductive tract, and play a very important and broad role in protecting the body from infections and responses to environmental insults,” says Belz...
“Thus, surprisingly, altering the balance of immune cells significantly affected what was happening in the cecum, suggesting that a similar effect might occur in humans in the appendix,” Belz says. “This highlights that simply disposing of this organ may not always be in our best interests.”
While the appendix is not required for digestive functions in humans, Belz tells mental_floss, “It does house symbiotic bacteria proposed by Randal Bollinger and Bill Parker at Duke University to be important for overall gut health, but particularly when we get a gut infection resulting in diarrhea.”
Infections of this kind clear the gut not only of fluids and nutrients but also good bacteria. Their research suggests that those ILCs housed in the appendix may be there as a reserve to repopulate the gut with good bacteria after a gut infection.ILCs are hardier than other immune cells, and thus vital to fighting bacterial infections in people with compromised immune systems, such as those in cancer treatment; they are some of the few immune cells that can survive chemotherapy." (HT: Uncommon Descent)
So it appears that another piece of evidence supporting Darwinian evolution may destined for the ash heap of history. In the future, we may find evidence that other vestigial organs really have a purpose as well.