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6.2 Builder Key Concepts A


Name Date Class

Key Concept Builder

The Theory of Evolution by Natural Selection

Key Concept

Who was Charles Darwin?


Directions: On each line, write the word or term that correctly completes each sentence.

Charles Darwin was an English 1.

who lived in the 1800s.

He was interested in plants and 2.

, and spent long hours studying their habitats. While serving as a naturalist on the British naval ship, the


, Darwin had the opportunity to study plant and animal life on the 4.

. What he found fascinated him.

The Galápagos Islands are found off the coast of 5.

in the

Pacific Ocean. Darwin found the environments on the Galápagos Islands quite different.

Some were 6.

. Some were more humid. Others were a mix of environments. Giant 7.

lived on the islands, but as Darwin learned, the tortoises on each island looked different. This made Darwin curious. Darwin also found that a variety of 8.

and finches lived on the

Galápagos Islands. He determined that he had come across several different

9. .

Darwin realized that a 10.

existed between species and food sources on the islands. Importantly, he recognized that the tortoise species were related. He believed they shared a common 11.

. But, why were they so different? Some tortoises had short necks; some had long necks. Darwin’s observations showed that tortoises with 12.

necks lived on islands with short grass. Tortoises with 13.

necks could stretch them and gobble the cacti growing on the island.

Darwin decided that the 14.

he observed were a key to how organisms evolve. He developed the theory of evolution by 15.


This theory says that populations of organisms with 16.

that help them survive in their environment live longer, compete better, and


more than those that do not have the variations. Darwin believed he found the understanding of how 18.

change as their environments change.

38 The Environment and Change Over Time