Peter Bowler has written some excellent books on the history of evolutionary biology. His text Evolution: The History of an Idea is a standard text, widely used. His The Eclipse of Darwinism was a really well-thought-out examination of evolutionary thinking in the period between 1859 and the rediscovery of Mendelian genetics in 1900, a period in which many biologists accepted evolution but rejected the notion that adaptation was the result of natural selection. His Life’s Splendid Drama covers the morphological studies of evolution by (mostly) German and English biologists between 1880 and 1920. A harder slog but well-researched. I jumped at the chance to get Darwin Deleted as a PDF. They do harvest your email address but that seems a small price to pay. (They have not yet sent me the link, though).