Darwin’s Model of Evolution
Charles Darwin was a naturalist who explored the South American coast in December of 1831. On the journey, he observed many plants and animals. He was amazed by the Galapagos Islands, which are about 1,000 km from the coast of Ecuador. Darwin hypothesized that the plants and animals on the Galapagos Islands might have come from Central and South America. He saw many species on the islands, however, that he did not recognize from South America such as giant cactus trees, huge land tortoises, and iguanas.
Darwin observed 13 species of finches on the Galapagos Islands. He noticed that all 13 species were similar, except for differences in body size, beak shape, and eating habits. He also noticed that all 13 Galapagos Island finches were similar to one finch species he had seen on the South American coast.
Darwin thought that the Galapagos finches had originally come from South America. He thought that they must have had to compete for food on the Galapagos Islands. Finches with beak shapes that allowed them to eat the available food would have survived longer and produced more offspring than finches without these useful beak shapes. Darwin thought that there might have been many generations of more and more finches surviving with the useful beak shapes until finally the groups of finches on the Galapagos Islands and the finches from South America were so far apart that they actually became different species.
The finches helped Darwin shape his theory of natural selection. He noticed that the finches had different beak shapes but resembled mainland birds and he hypothesized that they all had a common ancestor many generations ago. After he returned home from the voyage, he did some artificial selection with pigeons and found that traits from parents were passed to offspring, but with minor variations. Using his observations of finches (and many other Galapagos organisms) and his pigeon breeding experiments, he began to develop his theory that organisms can change their traits over many generations and become different species.