The scientist who proposed the theory of natural selection is Charles Darwin. In his groundbreaking work, “On the Origin of Species,” published in 1859, Darwin introduced the idea that organisms evolve over time through the process of natural selection, where individuals with advantageous traits survive and reproducibly pass on those traits to future generations. This mechanism explains the adaptation of species to their environments and provides a framework for understanding evolution. Darwin's theories revolutionized the study of biology and have since been supported by extensive evidence from genetics and fossil records.