The Expression of the Emotions in Man and Animals in the laying out of the sandwalk, his "thinking path", at Down House in Kent in 1846. These aspects of Darwin's personal life are discussed in John Bowlby's (1990) psychoanalytic biography of Darwin. Darwin emphasises a shared human and animal ancestry in sharp contrast to the arguments deployed in Charles Bell's "Anatomy and Philosophy of Expression" (1824). Bell claimed that the facial muscles were divinely designed in order to express uniquely human feelings. Eager to stress the differences between human and animal communication, Bell wrote: "Expression is to the passions as language is to thought." In "The Expression", Darwin reformulates
The Descent of Man, and Selection in Relation to Sex to the forces of sexual selection. While debates on the subject continues, in January 1871 Darwin started on another book, using left over material on emotional expressions, which became "The Expression of the Emotions in Man and Animals". In recent years controversy also involved the peacock tail, the most famous symbol of the principle of sexual selection. A seven-year Japanese study of free-ranging peafowl came to the conclusion that female peafowl do not select mates merely on the basis of their trains. Mariko Takahashi found no evidence that peahens expressed any preference for peacocks with more elaborate trains, such as