Not So Useless

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Science  23 Oct 2009:
Vol. 326, Issue 5952, pp. 503
DOI: 10.1126/science.326_503a

For humans, the value of having an appendix seems to be negligible and, given the prevalence of appendicitis, having an appendix can even be dangerous. This gut attachment has long been thought to be a remnant of the time when hominids ate a high proportion of plant matter that needed fermentation before digestion. More recently, the appendix has been proposed to play a role in the immune-mediated maintenance of symbiotic bacteria in the gut. On the basis of comparative anatomical and phylogenetic approaches, Smith et al. now contend that the appendix is a specialized organ for harboring symbiotic bacteria essential for health. Diarrhea was a common hazard during hominid evolution. Because the opening to the appendix is constricted, it may escape colonization by bacterial pathogens. Bacterial symbiont reconstitution after diarrhea can be achieved rapidly from the populations harbored in the appendix. Thus, far from being useless, positive selection may well have acted to maintain the appendix.

J. Evol. Biol. 22, 1984 (2009).

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