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4.7: Analogy vs. Homology

When I'm swimming in the ocean and see a vertical fin above the water in the distance, I always freak out and think it's whether it's a shark even though it always turns out to be dolphins. Dolphins evolved from a four-legged mammal that might have look something like a hippo, and the dolphin's fin and the shark's fin are coded for by totally different genes, and have a totally different evolutionary pathway. Traits that look the same but evolved separately are called analogies.

Homologies are traits that share a common evolutionary pathway, and the genes that code for them. The range of morphology of vertebrate forelimbs is incredible, but they all have the same genetic source, and thus share most of the same bones.

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Figure \(\PageIndex{1}\)Homologous vertebrate forelimbs 

When you see two species with similar traits, the first question is are they similar because they had the same ancestors (parallel) or they had different ancestors and evolved in similar environments.

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Figure \(\PageIndex{2}\)Parallel vs. convergent evolution

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Figure \(\PageIndex{3}\) - Convergent evolution for water