Charles Darwin (1809–1882) first proposed a theory of evolution based on natural selection in his treatise On the Origin of Species—a publication that ushered in a new era in our thinking about the nature of man. In fact, it is said that the intellectual revolution this work caused, and the impact it had on man’s concept of himself and the world, were greater than those by the works of English physicist Isaac Newton (1642–1727) and other individuals. The effect of the publication was immediate—the first edition sold out on the day of publication (November 24, 1859). Origin has been referred to as “the book that shook the world.” Every modern discussion of man’s future, the population explosion, the struggle for existence, the purpose of man and the universe, and man’s place in nature rests on Darwin.

The work was a product of his analyses and interpretations of his findings from his voyages on the HMS Beagle. In Darwin’s day, the prevailing explanation for organic diversity was the story of creation as told in the Bible’s book of Genesis. Darwin’s book was the first to present scientifically sound, well-organized evidence for the theory of evolution. The theory was based on natural selection, in which the best, or fittest, individuals survive more often than those who are less fit. If a difference exists in the genetic endowment among these individuals that correlates with fitness, the species will change over time and will eventually resemble more closely (as a group) the fittest individuals. It is a two-step process: the first consists of the production of variation and the second of the sorting of this variability by natural selection in which the favorable variations tend to be preserved.