Charles Darwin wrote a book called The Descent of Man In Selection in Relation to Sex, which was originally released in 1871. It describes his sexual selection theory, a type of biological adaptation that differs from natural selection yet is tied to it.Outlining how similar humans are to other animals is Darwin's strategy for supporting the evolution of people. He starts by drawing parallels between the anatomical structures, emphasizing body composition, embryology, and "rudimentary organs" that are presumed to have had a purpose in one of man's "pre-existing" forms.Darwin argued that there is no fundamental distinction between the intellectual, moral, and anatomical capacities of humans and those of other animals. Based on anthropology published since 1860, he assigned a hierarchical ranking to all aspects of life and extended it to include human races.The Sexes Throughout Nature, written by Antoinette Brown Blackwell and published in 1875, served as the foundation for Darwin's theory of evolution by natural selection. One of the first female critics of evolutionary theory, Blackwell said that it denied women their proper role in society.The majority of Descent is devoted to the discussion of sexual selection, which Darwin believed to be as important a theoretical contribution as his work on natural selection.