The appendix in humans is a vestigial organ. In other mammals, it is not vestigial and is larger because it helps to digest a certain type of plant material. Which statement most likely describes the appendix’s lack of function in humans?

An organ can become vestigial when the function it once served is no longer needed as much. Since the appendix helps other mammals digest certain plant material, humans’ reduced need to digest that material best explains why the appendix has little function in humans. Choice A, the human diet includes less plant material, fits this explanation.

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