In the next higher class, in birds, fertilization is internal, and only the development is external. The female bird has an ovary containing a large number of eggs or ova, within its body. The male animal possesses an organ serving for the introduction of the semen into the body of the female. The fertilized egg is laid and develops outside, either by the sun-heat or hatched by the mother’s warmth.
The last step in generation is reached in the mammals. Here not only fertilization is accomplished within the body of the female, but also the entire development of the fertilized ovum is carried out in the uterus, inside the female body. Hence mammals give birth to living mature young.
In these higher animals the attraction of the sex cells has been definitely transferred to, or rather changed into, the attraction of the hosts of these cells or into the sexual instinct. The sex-instinct is, therefore, if not identical with the instinct of propagation, thus an offshoot of the latter instinct.
In the more advanced species of the higher animals the instinct relating to the preservation of the kind is composed of three definite impulses. There is first the impulse relating to the act of conjugation, universal in all organic life. The average individual grows up surrounded by others of the opposite sex and normally unexcited by this difference until the age of puberty approaches. Then some day, the boy or girl find arising within an incipient impulse which, naturally, were there no artificial restrictions, would lead them to exercise their sexual powers, just as found among animals.
The second impulse relates to the pursuit and attraction of mates. It is first found among the lower types of the animal kingdom. The sweet odors and showy colors found in flowers are nothing else but the means of attracting the insects that carry the pollen for fertilization. The bright colors of some animals, especially among birds, and other animal adornments also serve to attract the mates. The woman’s love for finery also emanates from no other source than from the impulse of pursuit and attraction of mates.
The third impulse stands in relation to permanent mating and the protection of the young. It is the impulse relating to the germs of family life, and is present among those animals that have gained a higher place in the ascending scale of complexity and whose young are more difficultly provided for.[AA]
Through the whole range of animal life, where the period of infancy is comparatively short (e. g. horse, dog, cat, etc.), the male part is ended with impregnation or copulation. The nursing of the young is left to the female,[AB] and she will sacrifice her own life in the protection of her breed. In animals whose young are not easily provided for (e. g. fox, wildcat, eagle, sparrow, pigeon, stork, etc.), not only the mother will sacrifice her own existence in the protection of her offspring, but also the father will do his utmost in the interest of his young ones. In these animals the males remain attached to the females they have secured at the first period of oestrum even after the time of propagation has passed, provide mutually for their offspring until the latter can provide for themselves, and at each succeeding period of rut, yield again to love and never seek a new mate until the old one dies. Ernest Thompson Seton found that hawks practise monogamy and that wolves consort for life, and, in case of death, the survivor remains alone. The Canadian wild goose, when it has lost its mate, will never seek another. Thus the instinct of permanent mating or of monogamic marriage, is a phenomenon already found among many animals.
Now, among all animals, the prenatal period and the period of the maternal feeding are almost the longest in man. The helplessness of the human infant is unique among the creatures of the animal kingdom. The new-born baby is devoid of nearly all instinctive capacities, except the taking-in and assimilation of food. It is unable to stand or wander in search of food. It is nearly blind and deaf. It is perfectly naked, without fur or feathers, and hence is in need of a certain amount of heat, being injured by the least draught. It is in need of the utmost cleanliness, still it is unable to keep itself clean. It is unable to fast longer than a few hours. In short, the human infant is the most complete picture of helpless dependence. Hence without the help and strength of fatherhood, afforded to motherhood, the human race could not have survived the primitive stage, when couples still lived separated. The length and feebleness of human infancy required a union of male and female of considerable duration. By the time the last child was able to emancipate itself from the parental protection, the period of sexual activity had been passed. Permanent mating among men, especially in the prehuman stage, was a condition sine qua non, all the preachings of the free-lovers to the contrary notwithstanding.[AC]
Permanent mating is, therefore, a natural impulse among human beings. It is necessary for the protection and preservation of the lives of a lesser number of offspring of a higher grade. Permanent mating is, hence, of fundamental racial value. In man this impulse is of a more complex form and broader range, which leads the individual to wish not for momentary excitement, but for a permanent union, for a home, for a family. Even to the man who regularly indulges in meretricious venery there comes a time when these bonds of mere passion do not satisfy any longer. He begins to crave for a permanent mate and a home. This impulse appears later in life and is not present in the earlier impulse for mere conjugation, arising at the period of puberty. The amatory feelings at that time of life are bestowed upon the first pleasing individual of the opposite sex and are seldom of long duration. They are transferred from individual to individual. Later in life, after character is formed, there comes for men and women the dawn of a deeper affection, which involves bonds of stronger form and more permanent type than any that mere passion can arouse. This unconscious and involuntary craving for a permanent mate and home is of an altruistic nature. It has been wisely implanted in the interest of the race. There is nothing egotistical connected with this impulse. Personal gratification does not enter into consideration, for the joy and pleasure connected with personal satisfaction may be found with any temporary mate.