Part 1: The Evolution of Man
The first half of the book is devoted to an exploration of human evolution. Following up his infamous Origin of Species, Darwin is honing his theories in this volume. He explores the similarities between animal and human anatomy and psychology, concluding that humans are not a separate kind of being. He believes that humans are simply a more evolved version of animal life, still subject to many of the same behaviors. He further writes about the role of natural selection, genetic inheritance, and monogenism vs. polygenism. Apparently he favors neither theory, instead proposing the topic of the second half of the book.
Part 2-3: Sexual Selection
Darwin repeatedly writes throughout his career about how certain details of complexity among species have disturbed him. What evolutionary function could they serve? This question led him to propose the idea of sexual selection. This concept explains that females choose mates who demonstrate their value through attraction and evolutionarily dominant traits. Consequently males develop through competition, the successful ones developing superior traits. Darwin concludes that this "choosiness" on the female's part has led to her eventual inferiority to the more competitive and successful male.
