Homologous Structures

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Homologous structures are structures that are similar in shape and have similar uses. Species with homologous structures share common ancestry.

Vestigial Structures

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Vestigial structures are structures that are smaller and have less important uses such as the hind limbs on a whale or the appendix on a person. the fact that these structures exist suggest that animals with these structures have an ancestor with a species that used these structures for more important uses.