In humans, the diminutive appendix is, presumably, not functional or necessary for passing food through the digestive system. It is smaller than it is in other mammals, but the human appendix has a tendency to rupture and if it is not removed promptly a person can die as a result. One may wonder, then, why the appendix has not disappeared completely. There may be a function that is yet unknown, like during development in utero. Perhaps, however, the appendix is not disadvantageous enough for selection to act strongly against it and remove it from the human phenotype. Few people die of a ruptured appendix. And many of those who do have already reproduced and passed along their genes that include blueprints for building an appendix in their offspring.
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