But it was on the Galapagos Islands off the coast of Ecuador that Darwin found creatures that made him wonder about how species develop and change. There, he saw giant tortoises and noted that the reptiles were different on each island.

He collected birds, each with different beaks. Later, after he had returned to England, he would be shocked to find that these very different birds were all finches. Darwin found lizards called iguanas that lived on land and ones that fed in the sea.

Darwin noted that all these species were similar to those found in South America. But, they all had differences, or adaptations, that helped them survive in the environment of the Galapagos Islands.

STEVE EMBER: Darwin sent much of what he collected back to England on other ships the Beagle met along the way. By the time he returned to England in October of eighteen thirty-six, he was already a well known geologist and naturalist. Within a few years, he would be accepted into scientific organizations like the Geological Society and the Royal Society.

Darwin moved to London to be near other scientists. He wrote a new version of the book about his travels. He also edited works of others about the things he had collected on his trip. Darwin also agreed to write several books including the "Zoology of the Voyage of the H.M.S. Beagle." But in eighteen thirty-seven, the pressure of the work caused his health to suffer. He developed problems with his heart.