On the Origin of Species, published on 24 November 1859, is a work of scientific literature by Charles Darwin that is considered to be the foundation of evolutionary biology. Darwin's book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. It argues that the numerous traits and adaptations that differentiate species from each other also explain how species evolved over time and gradually diverged. Variations in organisms are apparent both within domesticated species and within species throughout the natural world.