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The wings of birds, the legs of pigs, and the flippers of dolphins are examples of vestigial fevers, homologous structures, acquired characteristics, artificial selection, or uniformitarianism.
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Let's go through and define these.
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First of all, a vestigial structure.
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So this is a structure that is not adaptive at the current point in time, but was adaptive in evolutionary history.
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So it's a feature left over from a time when it was adaptive.
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So for example, there are organisms that live in caves, and although there's no light, so they're blind, they may have vestigial eye structures, but are no longer functional, the evidence of a time in evolutionary history where their ancestors did have eyes and could see.
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The homologous structures, so these are structures that are similar because they were inherited, from a common ancestor.
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So the ancestor of the organisms had this trait, and they've all inherited it from it.
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They may have changed in form or function or size, but they're still very similar on a basic level.
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C, acquired characteristics.
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Acquired means it's something that the organism has gained within its lifetime...