Charles Darwin is known for the theory of evolution by natural selection. His groundbreaking work, "On the Origin of Species," published in 1859, introduced the concept that species evolve over time through a process where individuals with favorable traits are more likely to survive and reproduce. This theory challenged the prevailing views of the time and offered a scientific explanation for the diversity of life on Earth. Darwin's meticulous observations and research during his voyage on the HMS Beagle provided the foundation for his ideas. Today, his work remains a cornerstone of modern biology and has profoundly impacted our understanding of natural history.