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Charles Darwin's On the Origin of Species (published 1859) is a seminal work in scientific literature and arguably the pivotal work in evolutionary biology. The book's full title is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, while for the 6th edition of 1872 the title was changed to The Origin of Species. It introduced the theory that populations evolve over the course of generations through a process of natural selection. Darwin's book was the culmination of evidence he had accumulated on the voyage of the Beagle in the 1830s and expanded through continuing investigations and experiments after his return.

The book is readable even for the non-specialist and attracted widespread interest on publication. The book was controversial because it contradicted religious beliefs that underlay the then current theories of biology, and it generated much discussion on scientific, philosophical, and religious grounds. The scientific theory of evolution has itself evolved since Darwin first presented it, but natural selection remains the most widely accepted scientific model of how species evolve. The at-times bitter creation-evolution controversy continues to this day.

Summary of his theory

Darwin's theory is based on key observations and inferences drawn from them:[4]

1. Species have great fertility. They have more offspring than can grow to adulthood.
2. Populations remain roughly the same size, with small changes.
3. Food resources are limited, but are relatively stable over time.
4. An implicit struggle for survival ensues.
5. In sexually reproducing species, generally no two individuals are identical.
6. Some of these variations directly impact the ability of an individual to survive in a given environment.
7. Much of this variation is inheritable.
8. Individuals less suited to the environment are less likely to survive and less likely to reproduce, while individuals more suited to the environment are more likely to survive and more likely to reproduce.
9. The individuals that survive are most likely to leave their inheritable traits to future generations.
10. This slowly effected process results in populations that adapt to the environment over time, and ultimately, after interminable generations, these variations accumulate to form new varieties, and ultimately, new species.