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Vestigial things are non-working remnants of what once were working things. For example, a fruit fly with wings that are too small, whose ancestors had normal wings, is said to have vestigial wings. These leftover bits of organisms, like the human appendix in the digestive tract, are caused by genetically-encoded changes in development. Just because a thing existed in the past does not make it vestigial; there has to be some non-working or poorly working remnant today.