For finches on the Galapagos, a significant change in beak size can be observed across years with plentiful rainfall or intense drought.
How can the changes in finch beak size be attributed to evolution?
Finches on the island with better-adapted beak sizes have increased
survival
Finches on the island are domesticated and are artificially selected for
beak size.
Finches on the island without well suited beak sizes change their diet to
induce and enhance growth of their beaks.
Finches on the island reproduce with finches from nearby islands that have
larger beaks, resulting in changing beak sizes over time.
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Theory of Evolution
312 Natural Selection