Anatomical structures in different species that share a common evolutionary origin and similar underlying structure, regardless of their current function. They provide evidence of common ancestry.
From Greek 'homologos' meaning 'agreeing or corresponding' and Latin 'structura' meaning 'arrangement'. The term was introduced by comparative anatomist Richard Owen in 1843 to distinguish structures that share ancestry from those that merely share function.
The tiny bones in your middle ear used to be jaw bones in your reptilian ancestors millions of years ago! Homologous structures are like evolutionary recycling - nature takes existing parts and repurposes them for completely new jobs rather than starting from scratch.
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