New research offers some answers to the age-old question of why humans have an appendix.
For the study, published in the journal Comptes Rendus Palevol, researchers reviewed information on 533 species of mammals, some of which have an appendix and some of which do not. The list included a range of animals from around the world, with varying diets.
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The researchers found that the appendix evolved independently more than 30 times across different genetic trees—and it has hardly ever left a lineage after it appeared.
Lead study author Heather Smith, an anatomist at Midwestern University, said the researchers "failed to find a link between appendix presence (or size) and the dietary, ecological, and social characters."
What researchers did find was evidence that the appendixes serve a purpose, contrary to the conventional wisdom that "at one point we all needed them, [and] now people can get by just fine without them," Katherine Ellen Foley writes for Quartz.
Specifically, the researchers found that the appendix provides a secondary immune function that catalyzes immune cell responses. Smith explained, "In animals that have an appendix, there is a higher concentration of lymphoid tissue in the cecum," which connects the large and small intestine. Smith said the lymphoid tissue likely contains cells that trigger an immune reaction when the body is distressed.
The research also backs the idea that the appendix serves as a "safe house" of good bacteria for the body to use when the gut is cleared out—which happens when a person is taking antibiotics or has food poisoning.
According to Smith, the findings shouldn't cause concern for people who've had their appendix removed. She said the appendix provides a degree of immunity and beneficial bacteria, but that humans can still function without one (Foley, Quartz, 1/10; Marks, University Herald, 1/11; MacMillan, TIME, 1/11; Midwestern University release, ScienceDaily, 1/9).
As recommendations evolve, help your physicians consistently follow care standards
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