Charles Darwin's theory of evolution, published in 1859, changed how we understand life on Earth. Darwin suggested that species change over time through natural selection. This means creatures with traits better suited to their environment are more likely to survive and pass on these traits to their offspring. His ideas, explained in the book"On the Origin of Species", were based on his observations during his voyage on HMS Beagle. Darwin's theory remains fundamental to biology, explaining how different species evolve from common ancestors and adapt to their surroundings.