Kamis, 11 Oktober 2007

A Function for the Appendix?

It has long been thought that the small blind-ended pouch near the end of the small intestine called the appendix is vestigial, i.e. it no longer serves any useful function in humans. But now scientists at Duke University hypothesize that the appendix may indeed still have a function. In a September 7 article online in the Journal of Theoretical Biology, the researchers speculate that the appendix serves as a reservoir (or safe haven) for “good” bacteria in the event that a severe bout of diarrhea flushes out most of the bacteria in the small and large intestines. After the diarrhea has passed, according to the scientists, the bacteria in the appendix could emerge to repopulate the intestines.

It’s an interesting thought, but this is speculation, not yet proved. The Journal of Theoretical Biology is a vehicle for ideas, not hard scientific data. My question would be if the appendix does serve a useful function, why don’t most animals have one? (Apparently only humans, rabbits, and two species of marsupials have an appendix.) An admittedly equally speculative explanation might be that while the appendix does harbor bacteria that help repopulate the gut after a bout of diarrhea in humans, that function is not so significant that it confers significant survival value any more. In other words, the appendix ultimately still may be considered vestigial.

The concept of survival value of a given structure or function is an important one for students to understand when discussing evolution, of course.

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