The appendix is not a useless evolutionary artefact, researchers claim. Researchers at Duke University Medical Center had proposed two years ago that it actually serves a critical function — a safe haven where good bacteria could hang out until they were needed to repopulate the gut after a nasty case of diarrhoea, for example.
In a paper in the Journal of Evolutionary Biology, some of those same researchers along with collaborators from the University of Arizona and Arizona State University conclude that the appendix is a whole lot more than an evolutionary remnant. Not only does it appear in nature much more frequently than previously acknowledged, but it has been around much longer than anyone had suspected.
Their findings show that Charles Darwin was wrong.
“Maybe it's time to correct the textbooks,” says William Parker, the senior author of the study from Duke, said in a press release.
Using a modern approach to evolutionary biology called cladistics, which utilizes genetic information in combination with a variety of other data to evaluate biological relationships that emerge over the ages, Parker and colleagues found that the appendix has evolved at least twice, once among Australian marsupials and another time among rats, lemmings and other rodents, selected primates and humans. “We also figure that the appendix has been around for at least 80 million years, much longer than we would estimate if Darwin's ideas about the appendix were correct.”
Darwin theorised that the appendix in humans and other primates was the evolutionary remains of a larger structure, called a cecum, which was used by now- extinct ancestors for digesting food.
The latest study demonstrates two major problems with that idea. First, several living species, including certain lemurs, several rodents and a type of flying squirrel, still have an appendix attached to a large cecum which is used in digestion.
Second, Parker says the appendix is actually quite widespread in nature. “For example, when species are divided into groups called 'families', we find that more than 70 percent of all primate and rodent groups contain species with an appendix.” Darwin had thought that appendices appeared in only a small handful of animals.
“Darwin simply didn't have access to the information we have,” explains Parker. “If Darwin had been aware of the species that have an appendix attached to a large cecum, and if he had known about the widespread nature of the appendix, he probably would not have thought of the appendix as a vestige of evolution.”