Understanding Evolution

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

The tetrapod limb

Congratulations! You seem to already be an expert in homologies — you've selected all the homologous limbs. The four limbs you picked out all belong to tetrapods — animals with four legs.

Homologous Tetrapod Limbs

Notice how these tetrapod limbs are similar to one another:
  • They are all built from many individual bones.
  • They are all spin-offs of the same basic bone layout: one long bone attached to two other long bones.
Here you can see the same bones labeled in these different limbs:

Tetrapod limbs with bones highlighted

Download these (one and two of a series of six) graphics from the Image library.

Even though these limbs are similar to one another, the animals they belong to are quite different from one another. What animals possess these homologous limbs?


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