Charles Darwin is credited with formulating the theory of natural selection. His groundbreaking work, "On the Origin of Species," published in 1859, presented evidence that species evolve over time through a process where traits beneficial for survival and reproduction become more common in successive generations. Darwin's theory challenged existing beliefs about the immutability of species and provided a scientific explanation for the diversity of life on Earth. Natural selection remains a cornerstone of modern evolutionary biology, influencing not only science but also fields such as ecology, genetics, and anthropology, reshaping our understanding of life's complexities.