Charles Darwin developed the theory of evolution by natural selection, which posits that species evolve over time through a process where those best adapted to their environments are more likely to survive and reproduce. His groundbreaking work, "On the Origin of Species," fundamentally changed the understanding of biological diversity and the interconnectedness of all living organisms. Darwin’s theory challenged traditional views of creation and laid the foundation for modern biology. It sparked significant scientific and social discourse regarding human origins, prompting a reevaluation of humanity's place in the natural world.