Life and Letters of Thomas Henry Huxley, all three volumes in a single file Book

According to Wikipedia: "Thomas Henry Huxley PC FRS (4 May 1825 – 29 June 1895) was an English biologist, known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. Huxley's famous 1860 debate with Samuel Wilberforce was a key moment in the wider acceptance of evolution, and in his own career. Huxley had been planning to leave Oxford on the previous day, but, after an encounter with Robert Chambers, the author of Vestiges, he changed his mind and decided to join the debate. Wilberforce was coached by Richard Owen, against whom Huxley also debated whether humans were closely related to apes. Huxley was slow to accept some of Darwin's ideas, such as gradualism, and was undecided about natural selection, but despite this he was wholehearted in his public support of Darwin. He was instrumental in developing scientific education in Britain, and fought against the more extreme versions of religious tradition."