Although in such a case it was futile and often is harmful, the instinct of flight from danger is inherited from ancestors from a time when it served to save life. Attempts to escape are not the only signs of fear. There is often a trembling fit which would make flight impossible. In Mosso’s case of the Calabrian brigand, “after his struggles, cries and contortions, he fell on the ground in a motionless heap, like a wet rag; he became pale and trembled more than I have seen any other person tremble; his muscles seemed changed into a soft and quivering jelly.” This condition of trembling inertia is another legacy from animals. Quivering of the muscles often manifests itself in terrified animals. Darwin[158] wrote of it, “trembling is of no service, often of much disservice, and cannot at first have been acquired through the will, and then rendered habitual in association with any emotion.” The phenomenon seemed to him obscure and difficult to explain, a view shared by Mosso. The trembling of the musculature of the body is a generalised and exaggerated form of the movements of the cutaneous muscles in the condition known popularly as “goose-skin.” The latter, however, is a relic of an adaptation useful to some animals. The hedgehog rarely takes to flight at the approach of danger, but stands still, and using strongly developed muscles, rolls itself into a ball. In birds and many mammals, the muscles of the skin cause erection of the feathers or hairs. These movements often are performed during fright, and according to Darwin, serve not only to warm the skin, but sometimes to make the animal appear larger and more terrifying to enemies.
Fear and cold alike cause contraction of the superficial blood-vessels, and, in man, excite the contraction of the minute rudimentary muscles inserted to the roots of the hairs. “Goose-skin” is caused by the contraction of these muscles, the condition being a functional rudiment, no longer serving to warm the skin nor to make the body appear larger. In a few exceptional cases, “goose-skin” can be produced voluntarily. In the normal condition, the rudimentary cutaneous muscles of man are immobile, and it requires some special stimulation to set them in action.