What is homology and analogy? Biology

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Homologous structures are structures with simliar construction but not necessarily the same function. However, these structures indicate common ancestry. When one examines a bird wing, a frog limb and a human arm, one can see each bone although they may be modified due to natural selection for a particular use. The bird wing upon examination...

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Homologous structures are structures with simliar construction but not necessarily the same function. However, these structures indicate common ancestry. When one examines a bird wing, a frog limb and a human arm, one can see each bone although they may be modified due to natural selection for a particular use. The bird wing upon examination has the radius and ulna bones as seen in the frog limb and the human forearm. The bones of the wrist, hand and fingers are all there, although modified for flight, picking up something or for jumping. Analogous structures on the other hand, evolved along different evolutionary pathways to the same end. For example, if you observe a bat wing and a butterfly wing, they both serve the same purpose--flight. But, upon close scrutiny, the bat wing has muscles, bones, joints, skin, hair, etc. However, the wing of a butterfly is membranous, attached to an exoskeleton with a completely different design. These analagous structures do not suggest common ancestry.  

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