Forming a Theory

Darwin began to realize the effect of the birds’ isolation on the islands. It may have resulted in special adaptation. These changes happened slowly over time until new species were formed.

Darwin wasn’t the only scientist to be voicing this theory. Several naturalists had already developed this idea by the end of the 18th century. Darwin’s great contribution to science was that he was able to explain how and why evolution occurred.

 large ground finch

Española cactus finch

In 1859, Darwin published a book, On the Origin of Species. In it, he proposed that species evolve. He said that all living things can trace their descent back to a common ancestor.

Darwin also suggested a means by which we evolve: natural selection. This says that some plants and animals have traits that work best in a particular place. These living things are the ones that will survive and reproduce.

Over time, a population changes, or evolves, to better fit where it is. With enough time, however, a whole new species can emerge. Darwin’s thinking contributed to significant changes in how people saw the natural world. His contributions to science will always be remembered.