During his time as the ship's naturalist aboard the Beagle from 1831- 1836, Charles Darwin had the opportunity to study the wildlife of the Galapagos Islands. On the islands, he was amazed by the great diversity of life. Most particularly, he took interest in the island's various finches, whose beaks were all highly adapted to their particular lifestyles. He hypothesized that there must be some process that lead to such diversity and adaptation, and he spent much of his time trying to puzzle out just what the process might be. After returning from his voyage (bringing with him numerous dead finches, killed and stuffed at his behest), and at the urging of friends, Darwin put his thought in writing in a 490-page "abstract" that he entitled On the Origin of Species. He published the book in 1859.
The public reception of Origin was phenomenal. Within 15 years, it was well accepted that evolution did occur the way Darwin said, slowly and in small steps. However, the mechanism of natural selection remained difficult to accept at the time because there were many points Darwin himself admittedly could not explain. For example, he knew that traits were passed down from parents to offspring, but he did not know how this happened. It was not until the early 1900's, when the field of genetics became the focus of intense study that Darwin's mechanism of natural selection received more intense scrutiny and deeper scientific support. With the discoveries of genetics, Darwin's theories gained a scientific basis beyond observation and were consequently accepted as a plausible mechanism for evolutionary change. Even before genetics arrived on the scene, the idea of "survival of the fittest" captured the imagination of the public. The idea was applied to everything from the business world to the structure of society as a whole.