A
the founder species of finches on the Galapagos islands able to form such a large variation of beak types because the birds colonizing the islands were reproductively isolated.
Explanation:
The different founder species populations on the different islands could not mate randomly due to the distances between the islands. The reproductive isolation of the different populations caused the different populations to adapt to the conditions of their island (environment), by natural selection. Since every island has different environmental conditions, the different populations of finches evolved variable based on their island conditions.
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