The main factor of evolution Darwin called natural selection, and he drew his conclusions from observing, among other things, the process of domestication of wild animals.
Darwin also proved that the evolutionary principle applies not only to the biophysical but also to the psychological-behavioral development of living things and that there is no great gap between animal and human behavior. On the basis of a comparison of emotional movements in humans and animals, Darwin created the evolutionary concept of emotion.
He described his observations in his book The Expression of Emotions in Man and Animals (1872), which was a turning point in the understanding of the connection between biological and psychological phenomena, particularly the organism and emotions.
Davrin identified three principles that explain most of the expressions and gestures involuntarily used by humans and animals under the influence of various emotions and sensations:
I. The principle of useful associated habits.
II. The principle of antithesis.
III. The principle of actions conditioned by the structure of the nervous system, initially independent of the will and only to some extent independent of habit.
And he concluded that emotions appeared in the process of evolution of living beings as vital adaptive mechanisms, which help the organism to adapt to the conditions and situations of life.
I will give you just one example from this work, because the work itself is very interesting, and those who are interested in it, I think, will get acquainted with it independently …
“Man often scratches his head when he is in mental difficulty. I think he does this out of habit: it seems as if he is experiencing a slightly unpleasant and at the same time habitual itching sensation in his head, which he relieves in this way. The other rubs his eyes when confused or coughs when embarrassed, acting in both cases as if he were experiencing a slightly unpleasant sensation in his eyes or in his throat.
In most cases, these gestures and grimaces are of hereditary origin.
Judging from what we know of heredity, it is not improbable that any habits acquired by ancestors at a later age are manifested in the descendants who inherit these habits at an earlier age.