The Idea Of Evolution

After visiting the Galápagos Islands, Charles Darwin (1809-1882), shown in Figure 15-1, noted that groups of animals varied from island to island. For example, the tortoises on the same island resembled each other closely, but those from neighboring islands were different. Darwin noticed similarities and differences among many organisms as he traveled around the world. He became convinced that organisms had changed over time, and he wanted to understand why.

The development of new types of organisms from preexisting types of organisms over time is called evolution. Modern scientists also define evolution as a heritable change in the characteristics within a population from one generation to the next. Darwin sought to present the evidence that the evolution of new organisms occurs. Furthermore, he formed a theory to explain how evolution could occur. Others had tried to form such theories earlier, but Darwin's theory became the basis for modern explanations of evolution. Remember that in science, a theory is a well-supported explanation for some aspect of the natural world that incorporates many observations, inferences, and tested hypotheses. In forming his theory, Darwin took years to put together data from many sources and to take account of the ideas of other scientists of his time.

Ideas Of Darwin's Time

In Europe in the 18th century, most scientists thought that all species were permanent and unchanging. Furthermore, they thought that the Earth was only thousands—and not billions—of years old. However, scientists began to present evidence that the species on Earth have changed over time, and that the Earth is much older than anyone had thought.

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