On Natural Selection is one of the most important texts that make up The Origin of Species, the great book of Charles Darwin.

"Darwin's expression was very brief, and he confirmed the idea of the evolution of species by various evidences, and found a mechanism to make this evolution justified; he argued that life is like a tree, which grows from the root. The different shoots, the species, diversify over time, producing other species under the stress of certain conditions. […] In the century and a half between us and the publication of On the Origin of Species, the essence of its content It's just been confirmed again and again. There may be questions to figure out, but Darwinian evolution gives us a fundamental conceptual and explanatory framework that allows us to understand the natural world in a rational way without resorting to mythology."
—José Manuel Sanchez Ron, El País