"I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of anyone species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification."
Charles Darwin On the Origin of Species
On this day in 1859, Charles Darwin's On the Origin of Species was published in London.
Don't forget to give thanks to Darwin today for letting us stand on his shoulders.
Darwin's study at Down
More information on Darwin's writings and evolution:
Charles Darwin's writings on the web
Darwin Digital Library of Evolution
Darwin and Natural Selection