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Similarities and differences: understanding homology and analogy (High School level) :

Homology or analogy?

You have probably noticed that dolphins and sharks both have a streamlined body shape with a triangular fin on the back and two side fins. However, the two animals also have many differences.

Sharks Dolphins
shark dolphin
skeleton made of cartilage skeleton made of bone
use gills to get oxygen from the water in which they swim go to the surface and breathe atmospheric air in through their blowholes
don't nurse their young do nurse their young
don't have hair do have hair — they are born with hair around their "noses"

They may share the same basic shape, but underneath their skins, sharks and dolphins are very different!

Do you think that sharks' and dolphins' similarities (body shape, fin, and flippers) are homologies or analogies?
Shark photo provided Dong Lin © California Academy of Sciences; Dolphin photo provided by M. Winning © California Academy of Sciences

Homology & Analogy
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