The Origin of Species is one of the most controversial books of the 19th century. In it, the author, British naturalist Charles Darwin, argued that organisms gradually evolve through natural selection. Although the theory is widely accepted by scientists today, it is still banned in many schools (esp. in southern U.S. states) (see Scopes Monkey Trial). The full title of the book is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. It was first published on November 24, 1859 and immediately sold out its initial print run.
In it, Darwin presents a theory of evolution that is in most aspects identical to the theories now accepted by scientists. He carefully argues out this theory of evolution of species by natural selection by presenting all the accumulated scientific evidence from his voyage on the HMS Beagle in the 1830s. His theories were opposed to the then-accepted viewpoint of creationism. It is arguably one of the pivotal works in scientific history. Moreover, it was (and still is) eminently readable, even by the non-specialist (although it is very wordy - a good general level of intelligence is a prerequisite for comprehending the arguments and subtle nuances put forth by Darwin).
Darwin, as evidenced by his later work, The Descent of Man, was well aware of the implications such a theory would have on the study of the origins of humanity; consequently, he withheld publication of his accumulated evidence in favour of natural selection for more than a decade. He was eventually forced into publication because of the independent development of a similar theory by Alfred Russel Wallace, who sent Darwin his manuscript in 1858. A joint publication of Darwin/Wallace's theory of evolution was put forth the following year. It is felt by some that Wallace deserves as much credit as Darwin for the theory of natural selection, and that he has been rather unfairly marginalised from the history of its development.