The Expression of the Emotions in Man and Animals

Darwin's three principles are: (1) serviceable associated habits—expressions originally performed for practical benefit (squinting to protect the eyes) become habitual and then inherited; (2) antithesis—opposite emotions produce opposite postures through the same habitual logic (helplessness reverses the fight posture point by point); (3) direct action of the nervous system—extreme emotion produces surges of nervous energy discharged through whatever channels are available (tail vibration, trembling, blushing) . These principles matter because they are emphatically non-adaptive. Darwin does not argue that expressions survive because they improve survival; they persist because bodies are habit-forming and habit-inheriting. This distinguishes Expression from the Origin's adaptationism and has puzzled readers who expect Darwinian explanations everywhere .

Darwin obtained permission from Duchenne to reproduce several of his over 60 photographic plates showing electrically stimulated facial muscles . He praised Duchenne's method as a major advance and acknowledged his careful study of individual muscle contractions . But Darwin doubted Duchenne's view that separate muscle groups mediate dozens of discrete emotions. He wondered instead whether there might be a smaller set of core emotions expressed with great stability across cultures . Prompted by this doubt, Darwin conducted what may have been the first single-blind recognition study, testing whether associates could identify emotions from Duchenne's photographs—an experiment that anticipated contemporary cross-cultural emotion recognition research .

Darwin reasoned that if expressions are inherited evolutionary adaptations, they should be recognizable across cultures. He wrote to correspondents in the colonies asking how local peoples expressed feelings, and concluded from their replies that most expressions are universal . Ekman's editorial essay praises Darwin for being on the right track but identifies serious methodological flaws: the anecdotal evidence was unsystematic, Darwin may have presented only confirming cases, and his letters often posed leading questions (asking whether happiness wrinkled the eye rather than which emotion did) . Ekman nonetheless credits Darwin with initiating a research tradition that modern systematic methods have vindicated, showing that good science can be done in this field.

Italian psychophysiologists including Giuseppe Sergi, Angelo Mosso, and Giulio Camis engaged seriously with Darwin's work but found his physiological framework inadequate . Tebaldi noted that the second and third principles lacked evidence and required deeper scrutiny; Darwin seemed to lack understanding of the autonomic mechanisms underlying expression . Sergi criticized Darwin's explanation of blushing, arguing that circulatory changes were not effects of emotion but part of a more complex somatic process involving vagal and sympathetic pathways . The Italians saw Darwin's focus on macroscopic mimicry as methodologically distinct from their emerging experimental psychophysiology. Darwin worked when little was known about the autonomic system and paid little attention to vegetative variations later central to the field .

The Expression was published on November 26, 1872, and sold well, but it did not generate the controversy of the Origin . A German translation appeared that same year, Dutch and French versions in 1873 and 1874 . Second editions followed with minor alterations in 1890 . Yet the book was largely neglected through much of the twentieth century—some called it 'Darwin's forgotten masterpiece' . Its revival came largely through Paul Ekman's work on universality in the 1960s and 1970s, which cited Darwin as a precursor, and through Ekman's 1998 edition that restored Darwin's original notes and corrected the text . The book has never been out of print but only recently returned to prominence.

Denault and Zloteanu argue that body language experts have systematically misused Darwin's work to claim that non-verbal behavior is a universal 'language' that leaks authentic mental states, making it possible to 'read' anyone . They quote Darwin on involuntary muscles leaking expression while ignoring his broader argument about context and habit . This misuse has serious consequences: in police settings it can lead to coercive interrogation and false confessions; in security contexts, racial and religious profiling; in judicial settings, misinterpretation of honest testimony as deceptive, sometimes with life-or-death stakes in capital cases . The researchers conclude that non-verbal cues rarely have straightforward relationships with mental states and that the 'body never lies' premise is scientifically indefensible.