A 1997 display in the British Natural History Museum offered the following information on the Galapagos Island Finches:

There are countless different species alive in the world today. How were these species formed? Darwin's theory of evolution by natural selection offers a possible explanation. Let's look again at the way one species can become two and the part natural selection plays in the process. Suppose that one species is split into two separate populations by a geographic barrier. And the populations find themselves in different environments. Under the influence of natural selection, each population becomes adapted to the local environment. Because they are prevented from inter-breeding, over many generations the two populations gradually become different. Eventually they become so different that they cannot inter-breed, even if they have the opportunity to do so. The two populations become two different species.

Some of the best evidence to support this theory has been found where geographic barriers are particularly obvious—for example, where the sea forms the barrier between animals living on different islands. And it was on a group of islands in the Pacific Ocean that Darwin discovered some of the most important clues to his theory of evolution. Those islands were the Galapagos Islands. Here Darwin found very many strange plants and animals. Many reminded him of those he had seen on the main land, but some of them were very different. Animals and plants like these were found no where else in the world.

This started Darwin thinking about the process of evolution. In particular, he was intrigued by a group of thirteen different species of finches. All of the finch species of the Galapagos Islands were very similar, but each one had a different size or shape of beak. The different beaks are adapted to eating different kinds of food. Some of the finches have large, strong beaks, and can crush hard shells or seeds. This finch [in display] has a long, thin beak and uses it like a pair of tweezers to get its food. The woodpecker finch goes one stage further and sometimes uses a cactus spine to poke insects out of holes in tree trunks. Between them, the finches of the Galapagos Islands enjoy a most varied menu. So how were all these finch species formed?

Perhaps the history of the islands themselves provides a clue. Geological evidence suggests the Galapagos Islands rose up out of the sea as volcanoes a few million years ago. Gradually, they became colonized by plants and animals from the main land. Suppose a few stray finches were blown off course by a strong wind and managed to reach one of the islands. Here they would find new surroundings and new kinds of food to eat. Over many generations, the finches would increase in number and gradually, under the influence of natural selection, become adapted to their new environment. After a time, some of the finches might manage to fly to a near-by island with different habitats and different kinds of food. The finches are now split into two groups with the sea as the geographic barrier.

Over further generations the individuals of the second colony would gradually become adapted to their new environment. Eventually, some of the finches from the second island might find their way back to the first, but they are now so different from the original finches that the two groups cannot interbreed. Two different species have evolved.

Over many thousands of years, the finches colonize the other islands, and more new species were formed. Today there are thirteen species of finches on the Galapagos Islands. And they remain one of the best examples of evolution involving natural selection.