Charles Darwin proposed the theory of natural selection, which he introduced in his seminal work "On the Origin of Species" published in 1859. This theory explains how species evolve over time through a process where individuals with advantageous traits are more likely to survive and reproduce, passing those traits to the next generation. Darwin's observations during his voyage on the HMS Beagle, particularly in the Galapagos Islands, provided evidence for his theory. Natural selection remains a fundamental concept in biology, influencing our understanding of evolution and species adaptation.