This chapter introduces the central ideas in Darwin’s Expression, poses the main interpretive questions that scholars have raised, and outlines my answers to those questions. Why does Darwin analyze expressions in terms of heritable habits, recalling Lamarck’s debunked theory of evolution, when his own theory of natural selection provides a superior alternative? My answer is that Darwin embraces Hartley’s associationist theory of mind, which posits habit as the basis of thought. I claim that multiple puzzling features of Expression are resolved once we view Darwin as an associationist philosopher.

This chapter argues that Darwin’s philosophical theory of emotion has been forgotten due to paradigm shifts in biology, psychology, and philosophy. These shifts have caused researchers to neglect associationist theories of emotions, including Darwin’s contributions to this school of thought. Having explained why Darwin’s philosophy was forgotten, I conclude by explaining why it should be remembered, given its relevance for contemporary emotions research.

This chapter traces the development of Darwin’s theory of emotion and expression from 1838 to 1872, emphasizing his many engagements with associationist philosophers. I demonstrate that all three of Darwin’s principles of expression are derived from the works of associationist philosophers, especially David Hartley, Erasmus Darwin, Herbert Spencer, and Alexander Bain.

This chapter examines Darwin’s analysis of emotional expression. It is widely accepted that Darwin wrote Expression to refute Sir Charles Bell’s theory that God created humans with special muscles to express their emotions. However, scholars have overlooked the fact that Bell developed his theory to refute Erasmus Darwin’s associationist analysis of emotional expression, inspired by David Hartley, and that Charles Darwin defends his grandfather’s analysis against Bell’s objections. I demonstrate that Charles’s defense of Erasmus’s associationist theory, which denies that expressions occur for the sake of communicating emotions, explains Charles’s puzzling reluctance to claim that expressions evolved to serve as signals in communication.

This chapter is the first of two on blood as a figure for kinship and species identity in the nineteenth century. It begins with the history of bloodletting and blood transfusion in the period, and documents the emergence in the second half of the century of an imaginary species body, whose individual members are characterized by their propensity to save or waste blood from the common supply. The idea of a collective body sharing a common blood is traced in a series of texts on bloodshed and blushing, including Alfred Tennyson’s “Maud,” William Morris’s “The Defense of Guinevere,” Christina Rossetti’s “The Convent Threshold,” D. G. Rossetti’s “Jenny,” and Darwin’s Expression of the Emotions in Man and Animals.