Darwin from Descent of Man to Emotions under Domestication" which went on sale on 30 January 1868. He now published his ideas on human evolution and on how beautiful but apparently impractical features could have evolved in "The Descent of Man, and Selection in Relation to Sex". After revising "The Origin of Species" as the definitive 6th edition, his major works on species culminated in "The Expression of the Emotions in Man and Animals". This period was followed by extensive work on insectivorous plants and research into worms. Despite Darwin's concerns that his children were weakened as his wife Emma Darwin was his cousin or had inherited
The Expression of the Emotions in Man and Animals initial correspondence with the psychiatrist James Crichton-Browne Darwin set aside his material concerning emotional expression in order to complete "The Descent of Man", which covered human ancestry and sexual selection. Darwin concluded work on "The Descent of Man" on 15 January 1871. Two days later, he started on "The Expression of the Emotions" and, on 22 August 1872, he finished work on the proofs. In this book, Darwin brings his evolutionary theory into close approximation with behavioural science, although many Darwin scholars have remarked on a kind of spectral Lamarckism haunting the text of the "Emotions". Universal Nature of Expression: