Charles Darwin is best known for his theory of evolution, which he outlined in his groundbreaking work "On the Origin of Species" published in 1859. Darwin proposed the mechanism of natural selection, suggesting that species evolve over time through a process where individuals with favorable traits are more likely to survive and reproduce. His ideas challenged the prevailing views of species creation and sparked significant debate in scientific and religious communities. Darwin's work laid the foundation for modern evolutionary biology and continues to influence the understanding of the diversity of life on Earth.