Charles Darwin was a British naturalist whose scientific theories revolutionized biology.

His five-year voyage on HMS Beagle, particularly his observations in the Galápagos Islands, provided crucial evidence for his theories.

In 1859, he published his groundbreaking book, 'On the Origin of Species.'

The book proposed the theory of evolution by natural selection.

The theory has two main components: all life has descended from a common ancestor (evolution), and the primary mechanism for this change is natural selection.

Natural selection is the process where organisms with traits better suited to their environment are more likely to survive and reproduce.

This concept is often summarized as 'survival of the fittest.'

Darwin's theory provided a scientific explanation for the diversity of life on Earth, without recourse to divine creation.

His later book, 'The Descent of Man,' applied his theory to human evolution, which was highly controversial.

The theory of evolution by natural selection remains the foundational principle of modern biology.