In 1872, thirteen years after he published his most famous book, The Origin of Species [DARWIN 1859], Charles Darwin published a more obscure book, The Expression of Emotions in Animals and Man [DARWIN 1872]. This book bolstered his theory since, as his biographers say "Any sympathetic observer could see that man and animals shared not only feelings, but the means of expressing them." [DESMOND & MOORE, Page 593]. One of the recent re-publications of this book contains an Afterword by Paul Ekman summarizing the research in this domain since its first publication.

Ekman concludes that Darwin had got the principles that govern such non-verbal communication of emotion essentially correct [EKMAN]. He himself had conducted research in many diverse cultures and discovered that the facial expressions corresponding to the basic human emotions were universal. Not only did a member of a remote tribe in New Guinea make the same expressions but could identify the emotions expressed by a Caucasian even though Paul Ekman was the first white man he had met. Since we are all members of the same species with a shared evolutionary history, we share the same emotions and express them in the same way. Since it is of evolutionary value to recognize faces, and to read the emotions they express, it is not surprising that there is an area of the brain dedicated to facial recognition, and that no one ever says "I remember your name but I can't place your face".

There are many practical applications of this theory, originated by Darwin and refined by Ekman. Lie detectors are not admitted in courts, but Paul Ekman is often consulted as a lie-detector to detect lies in videotaped speech. He is also consulted by actors, who simulate emotions - when asked what he does for a living, Clint Eastwood says "I make faces". Paul Ekman, who has mastered the control of the various muscles which create the faces corresponding to the various emotions, can teach them to make the appropriate faces. As animation gets more and more realistic, animators must learn how to simulate the various human emotions.

Darwin did not consider language. He was focussed on what animals and humans had in common. The expression of emotions in animals and humans is dramatically similar, as he brilliantly demonstrated. However, he did not go beyond non-verbal communication to verbal communication. Language is what best distinguishes us from the other animals. Let us look at the work of two evolutionary psychologists who help fill in this "missing link" in the theory of evolution.