As a sequel to The Origin of Species, Charles Darwin's The Descent of Man, and Selection in Relation to Sex Analysis lives up to the expectations. Darwin very obviously continues to develop his theories of evolution and selection which he first introduced to the world in his magnum opus. This volume has a dual focus: the evolution of homo sapiens and sexual selection. Building upon pre-existing ideas and the most accepted theories of biology, anatomy, and psychology of his day, Darwin works out a more cohesive understanding of human evolution and biological programming.
The first half of the book addresses the evolution of man. Darwin records pages and pages of notes from anatomical dissections of various animals. In an attempt to explain the similarities between all species, he theorizes that indeed all mammals have a common ancestor. Interestingly this theory is aggregated a bit later to explain the existence of racial diversity among humans. This is an issue for which Darwin has been greatly criticized in succeeding generations. Although he presents both monogenist and polygenist arguments, he doesn't ever decide in favor of either camp. Instead he proffers that natural selection in the form of climate adaptions is most likely the reason for the extreme diversity among human races. This idea builds upon his previous argument that humans are not altogether that different than apes because "civilized" behavior is a loosely veiled continuance of ape culture.
Parts II-III address sexual selection. Apparently this concept had plagued Darwin for sometime because the idea of sexual selection had never before been theorized yet Darwin's own theory of evolution could not account for the complexity and beauty of many adaptions among the animals. For example, why is the peacock's tail so elaborate? Understanding it could prove a hinderance instead of an asset to the fowl, Darwin pondered the question for sometime before realizing that these troublesome features, like the tail, appear almost exclusively in the males of each species. That was the key to unlock the world of sexual selection. Basically Darwin's theory breaks down into the selectiveness of the females and the consequent competition among males. This is another point, however, where Darwin has received much criticism. He elaborated the theory by attributing his assumptions about male superiority to the "choosiness" of the females, a trait which he claims eventually led to their inability to compete.
