Charles Darwin is credited with developing the theory of evolution by natural selection. His groundbreaking work, particularly highlighted in his book "On the Origin of Species," published in 1859, established that species evolve over time through a process where individuals that are better adapted to their environment tend to survive and reproduce. This concept revolutionized biology and provided a unifying framework for understanding the diversity of life on Earth. Darwin's observations from his voyage on the HMS Beagle, combined with thorough research in various fields, laid the foundation for modern evolutionary theory, which continues to be supported by extensive scientific evidence.