Charles Robert Darwin was an English naturalist, geologist, and biologist who is widely known for his contributions to evolutionary biology. He proposed the theory of evolution by natural selection which has become a fundamental concept in science. His five-year voyage on HMS Beagle established him as an eminent geologist whose observations and theories supported Charles Lyell's concept of gradual geological change. In 1859, he published his book On the Origin of Species which contained compelling evidence for his theory and subsequently gained widespread acceptance from the scientific community. Darwin's scientific discovery is now considered the unifying theory of life sciences, explaining the diversity of life that exists today.