Between these two extremes there is, however, one important domain, viz., that of _recent phylogeny_, or in other words _variation_. The fixed appetites and instincts of the species which are proper to every normal man, and are as we have seen fundamentally connected with many animal forms, belong to ancient and profound phylogeny. But there is another group of very variable peculiarities, strongly developed in some men and little in others, sometimes completely absent, which do not depend on custom but on what is called individual hereditary disposition, or individual character. While some men have monogamous instincts others are polygamous. Some men are by instinct and heredity very egoistic, others more altruistic. This peculiarity is reflected in their sexual life and changes the character of their love (but not that of their sexual instinct). The egoist may love his wife, but this love is interested and very different from that of the altruist. Between the two extremes there is an infinite number of gradations according to the nature of the instincts and dispositions. The same man may be a good and generous father, and a social exploiter with neither shame nor pity. Another will pose as a social benefactor, while at home he is an egoist and a tyrant. The individual dispositions of recent phylogeny are combined in every way with education, customs, habit and social position to produce results which are often paradoxical, and the factors of which are ambition, vanity, temper, etc. Recent phylogeny is reflected also in many of the irradiations of the sexual appetite of which we have spoken in Chapter V. Audacity, jealousy, sexual braggardism, hypocrisy, prudery, pornography, coquetry, exaltation, etc., depend in each particular case, according to their degree of development, on a combination of individual sexual hereditary dispositions with individual dispositions in the other domains of sentiment, intelligence and will. In this way, the sexual individuality of one man is constituted in a very complex and very different way to that of other men, owing to the high development of the human brain, as well as to the infinite variability and adaptability of his aptitudes. It is impossible to give even an incomplete explanation of all the symphonic gradations (often cacophonic) which represent an individuality, or to fix clearly what distinguishes it from others. However, when the principle is understood, it is not difficult to estimate the sexual individuality of each person more or less correctly.