This is the only situation in the life of the lower animals, at any rate, where the choice of another is vitally important; and corresponding with the elaborate technique to secure this choice we have in wooing pleasure-pain reactions of a violent character. In a word, extreme sensitiveness to the judgment of another answers on the subjective side to technique for the conquest of a member of the opposite sex. It seems, therefore, that we are justified in concluding that our vanity and susceptibility have their origin largely in sexual life, and that, in particular, our susceptibility to the opinion of others and our dependence on their good will are genetically referable to sexual life.
This view would be completely substantiated if we could show that the qualities of vanity and susceptibility in question are present in any species where it is impossible to assume that they were developed in connection with the struggle for food and as the result of the survival of types showing a tendency to combine and co-operate in the effort to get food. And we do, in fact, have cases of this kind among some of the lower animals. It cannot be said that the dog, for instance, has survived in the struggle for existence because of his sensitiveness to public opinion in his species nor on account of an interest in being well thought of by the community of dogs at large which would lead him to behave in a public-spirited or moral manner. At the same time, the dog in his relation to man shows as keen a sensitiveness to man's opinion and treatment as does man himself. The attention which the master pays to one dog will almost break the heart of a dog not receiving it. A neglected dog plainly suffers as much in his way as the soldier who is sent to Coventry by his messmates; and if neglected and jealous dogs do not commit suicide, as they are reported to do, they are evidently in a state of mind to do so. This means that the dog has highly developed susceptibility to the appreciation of others, and that the species which he represents has had no history except a sexual history capable of developing this mental attitude. In connection with courtship he developed a fund of organic susceptibility, and this condition is involved in his more general relation to man; the machinery set up in sexual relations is played on by stimuli in general. A condition favorable to stimuli of a particular kind is favorable to stimuli in general; and it seems likely that this not very prominent fact of a state of excitation in a sexual connection is an important factor in the formation of the mind and of society.