Charles Darwin: The Origin Years (1836-1859).

The article focuses on Charles Darwin's intellectual development and scientific work from his return to England in 1836 through the publication of *On the Origin of Species* in 1859. It details Darwin's evolving ideas on species transmutation and natural selection, influenced by his observations during the Beagle voyage, his extensive study of barnacles, and his reading of Malthus' essay on population. The article also highlights Darwin's personal struggles with religious belief, family losses, and health issues, as well as his collaboration and simultaneous discovery of natural selection with Alfred Russel Wallace. Ultimately, Darwin's *Origin* provided a comprehensive, well-supported theory of evolution that linked life sciences with earth sciences and had a profound impact on scientific thought.