Charles Darwin's ideas and observations about how life evolves on Earth led to the development of a theory, not a law. Darwin's theory of evolution by natural selection, outlined in his book "On the Origin of Species," proposed that species change over time through a process of gradual modification and adaptation. This theory explains the diversity of life on Earth and the patterns of similarities and differences among species. It is supported by a vast amount of evidence from various scientific disciplines, including paleontology, genetics, and comparative anatomy. The theory of evolution by natural selection is widely accepted in the scientific community and forms the foundation of modern biology.