The significant scientific theory proposed by Charles Darwin is the theory of evolution through natural selection. In his landmark work, "On the Origin of Species," published in 1859, Darwin argued that species evolve over time due to environmental pressures that favor certain traits, leading to survival and reproduction. This theory fundamentally changed the understanding of biological diversity, suggesting that all life shares a common ancestry and that adaptations arise in response to the challenges of the environment. Darwin's ideas were initially controversial, but they provided a scientific framework for understanding the development of life on Earth, influencing multiple fields, including biology, genetics, and anthropology.