During his visit to the Galapagos Islands Charles Darwin saw that each island was populated by finches. These birds were all very similar, yet from one island to another there were some differences in the size and shape of the beak. Darwin  concluded that in the past a pair of these birds had been blown 600 miles from the mainland and the off-springs "evolved" into all the other types he saw.

Illustration: Darwin’s finches. (PD)