Three Evolutionary Principles of Expression

The chapter's central question

A useful associative habit is a behavior that has been helpful in a particular situation in the past and is repeated under similar conditions. The principle of opposition explains the tendency for opposite states of mind to be expressed in opposite postures, and the direct action of the nervous system explains tremors and secretions that are not controlled by the will. The three principles are not a simple table that corresponds to each facial expression, but rather an explanatory framework that can overlap with each other.

Read the complete essay

Darwin clearly explained why certain emotions cause certain physical reactions in three principles.

� 1) Principles of useful association habits:

Why do we open our eyes and open our mouths when we are surprised or scared? This is to maximize your viewing angle to identify danger in the dark, and get ready to run by breathing in oxygen into your lungs all at once! On the other hand, when you feel 'disgust', you wrinkle your nose and stick out your tongue, which originates from the vomiting reflex to block the smell of spoiled food and spit it out.

� 2) Principle of Opposition:

When attacking an enemy, a dog stands upright and growls, but in front of its loving owner, it lowers its body and wags its tail. Opposite emotions convey clear signals without misunderstanding through opposite body postures.

� 3) Direct action of the nervous system:

Trembling hands or pouring out cold sweat under extreme tension are physiological discharge valves that allow explosive energy to boil over in the body and be released out of the nervous system.

Context and nuance

Darwin's 『Expression of Emotions in Man and Animals』 studied facial expressions and gestures not as created fixed symbols but as behaviors formed throughout the history of the species. Comparing babies, animals, photographs, works of art, and reports from different parts of the world, he argued for the continuity between humans and other animals.

The explanation that all expressions are adaptations of the present is simpler than Darwin's own position. Some expressions may be the by-products of once useful habits, or they may be the direct result of excessive nervous excitement. Evolutionary explanations require comparative evidence rather than the plausible argument that ‘this facial expression was clearly designed for this purpose’.

Do not oversimplify it this way

Knowing our evolutionary origins does not always make our current emotions useful or commands to follow. Reactions formed in past environments may be at odds with today's situations, and cultural learning and individual differences play a large role on universal trends. Darwin's historical data and the conclusions of today's emotional science must be read separately.

Philosophy in life

Have you ever felt so pitiful that the mere sound of a rustle in a dark alley made your hair stand on end and your heart pound like it would explode?

Making room for tears: If tears come, you do not have to hide them, but there is no requirement to cry to feel better.

Primary-source guide

Primary guide: The Expression of the Emotions in Man and Animals, especially chapters 1–3 and 8–14.

Pathos Editorial · Reviewed 2026-09-12