One of the most important books in the history of science is entitled "On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life".
It was written by Charles Darwin, an English naturalist and first published in 1859.
Although it was by no means the first book about evolution (evolutionary theories were already common by the mid 19th century, and in fact dated back to atleast the 6th century BCE), what it did do was present the idea of evolution to a wider public, and make them aware of Darwin's explanation of the mechanism by which evolution occurs, namely natural selection.
The origins of the book can be traced back atleast 30 years.
When Darwin was at the University of Cambridge in the late 1820s (if not even earlier) he became aware of Uniformitarianism (the idea that the same principles operated in the geological past as in the present), and of the great age of the Earth.
Later, during the years 1831 to 1836, Darwin participated in a great nautical voyage around the world on HMS Beagle, and this to contributed to the development of his ideas.
On his return to England, Darwin gradually began to develop his theory of evolution by natural selection.
The idea behind this theory is surprisingly simple: favorable heritable traits tend to become more common in successive generations of a population, and unfavorable heritable traits less common, because favorable traits lead to greater success at reproduction.
Over immense periods of time, this allows organisms to evolve adaptations to their environments, and can result in the creation of new species.