Darwin's observations on the beaks of finches, which shaped his theory, were made on the

Explanation

During the voyage of HMS Beagle Darwin found that each island of the Galapagos group carried finches whose beaks matched the food available there, from heavy seed crushers to fine insect probes. He later realised they had descended from one mainland ancestor and diverged, which is the classic example of adaptive radiation. The other island groups have famous endemic species but were not visited by the Beagle.