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Cover Story

Grades 4-6

Darwin's Big Idea

Martha Pickerill

Charles Darwin was born 200 years ago this month. In 1859, his book On the Origin of Species set forth his theory of evolution on how living things change over time to survive.

When Charles Darwin was 22, he set out on a remarkable five-year voyage aboard the HMS Beagle. Darwin's job was naturalist, or biologist. At every stop, he collected fossils and animal specimens, and kept careful records of his natural surroundings.

He compared fossils with modern species. He studied physical differences between similar animals living in different environments. Darwin used his findings to make the case for natural selection or survival of the fittestothe idea that animals with the best traits for survival have offspring and continue the species. Weaker animals are less likely to survive and pass on their traits. After thousands of generations, nearly every member of a species is born with the traits that make it a good survivor.

The Animals of the Galápagos

On the Galápagos Islands (see map), finches were one of Darwin's best examples. The birds on each island had beaks of different shapes and sizes, depending on their food source. Finches that ate cactus fruit had small, narrow beaks. Finches that ate hard seeds had larger, stronger beaks to crack open seed shells.

Since Darwin's theory was published, the evidence of evolution has grown. Darwin would be proud that his theory has given scientists a new way of looking at the world.

"We can dimly foresee that there will be a considerable revolution in natural history," he wrote in 1859. He did not see his work as the final word but as a new beginning.

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