Charles Darwin's theory of evolution, expressed in the book, "The Origin of Species," radically changed thinking about how species evolve and change. Up till that point, the prevailing theory was Jean Lamarck's conclusion that animals acquired (or lost) traits through use during their lives, and then passed those acquired traits to their offspring.

Charles Darwin's Journey

In 1831, Darwin began a five-year trip aboard the H.M.S. Beagle, on a voyage to South America and the South Pacific. While in the Galapagos Islands, he noted the number of different bird species on the islands and tried to account for their diversity. He believed that the difference could be accounted for by the birds' adaptation through natural selection to the differing environments of the islands.

Underlying Principles

Darwin's theory of evolution is based on the idea that there is genetic variety in every population. Species process more offspring than can survive, forcing competition for limited resources. Individuals that have beneficial traits are more likely to survive and therefore more likely to reproduce and pass on their genes.

Natural Selection

Natural selection means that the individuals best suited to an environment are the most likely to survive and reproduce in it. An individual with a genetic mutation that allows them to collect food more easily, for example, makes them more likely to survive than an individual lacking the same mutation. Such mutations are "selected" by natural circumstances of their environment.

The Origin of Species

In the 1850s, Darwin began writing a book explaining his theory of evolution. Another scientist, Alfred Russel Wallace, working separately, sent Darwin an essay that mirrored Darwin's conclusions. Darwin presented his and Wallace's theory together to other scientists, but the theory roused little reaction until the 1859 publication of "The Origin of Species," in which Darwin thoroughly explained his conclusions.

Public Reactions

Reactions to the theory advanced in "The Origin of Species" were widespread and sometimes indignant. Opponents of Darwin misrepresented his theory and claimed that he was saying that humans were evolved from monkeys, but the theory took root in the scientific community quickly.

Source:

SpaceAndMotion.com: The Theory of Evolution

Palomar Community College: Darwin and Natural Selection

More Information:

National Science Teachers Association: Resources for Teaching Evolution

University of California Museum of Paleontology : Teaching Evolution