The Origin of Species by Means of Natural Selection
On The Origin of Species by Means of Natural Selection is a book by Charles Darwin published in 1859. It introduced the world to evolution through a process of natural selection. The main thesis was that different animal species were not independently created, and that similar species can result from natural variation followed by different survivability rates. Animals that are more adapted to their environments are more likely to survive. Alfred Russel Wallace wrote a similar theory independently, and had sent a manuscript to Darwin. Darwin also used Herbert Spencer's phrase "survival of the fittest", but then fitness has to be defined as that which survives.
Human evolution is conspiculously absent from Origin - knowing of the opposition such a suggestion would face, Darwin confined his initial speculation to animals.