Similar anatomical structures may be due to homology, which means the structure was inherited from a common ancestor that already had that structure. Humans and sharks both have hearts and two eyes because their last common ancestor did.
Similar anatomical structures may also be due to homoplasy, which means the structures independently evolved in each lineage. Hippos and alligators both have eyes and nostrils on the top of their head, independent adaptations to living mostly submerged in water.
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