A bird's wing and a butterfly's wing do the same job, so why are they NOT evidence of common ancestry?
They are analogous, not homologous.
They are analogous, not homologous. A bird's wing is built on a forelimb skeleton, while a butterfly's wing is a thin, boneless extension of the body wall -- completely different structures that reached the same function, flight, independently. This is convergent evolution driven by a shared need, not by a shared ancestor. Only homologous organs, which share underlying structure, point to common ancestry.
Key point
Bird and insect wings are analogous (same function, different structure) -> convergent evolution, not common ancestry.
Common mistake
taking any shared function as proof of a common ancestor.
Memory tip
same job but different build = analogous = convergent (no shared ancestor).
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