From the phylogenetic point of view we can only compare ourselves to the higher apes, by their analogies with primitive man. (Vide Chapter VI.) The question which concerns us here is as follows: If we consider the peculiarities of our sexual customs with those of our direct ancestors, what are those which are derived from ancient and profound phylogenetic instincts, those which are derived from less profound ancestral energies (_i.e._, relatively more recent) and lastly those which depend simply on old customs fixed by tradition, prejudice and habit? If we are careful we shall immediately recognize that it is not only the sexual appetite itself, but also a large part of its correlatives and irradiations, in which the phylogenetic roots are deep. Jealousy, coquetry, instinctive maternal love, fidelity and conjugal love, which are more or less developed in primitive man, are also present in monkeys and birds. We have even seen that the conjugal fidelity of these often exceeds our own. It is, therefore, not true that our animal ancestors are only allied to us by sexual appetite; on the contrary, we must admit that they have much more noble sentiments and instincts, derived it is true from this appetite, but belonging to the domain of a higher social morality. All that we can say in a general way concerning the complex entanglement of our sentiments and instincts is that, the most deeply rooted characters in human nature are at the same time, phylogenetically speaking, the most ancient. Among the most profound instincts of sexual life, we find moral and intellectual incongruities. Along with excitement of the sexual appetite in the male by the odor of the female genital organs, or by the sight of erotic pictures, we find the most touching conjugal love, and life-long devotion of one conjoint for the other and for the children. Prostitution, marriage by purchase, religious marriage, disgrace attached to illegitimate births, conjugal and family rights of one or the other sex, etc., are, on the contrary, things which do not depend on recent phylogeny, but only on the customs and traditions of certain races. They are partly outgrowths from egoism, the spirit of domination, mysticism and hypocrisy, and partly the shifts of an overheated social life which is becoming more and more complicated. Westermark's studies are very instructive in this respect. All the absurdities and contradictions, brought to light by the historical and ethnographical study of the customs and matrimonial abuses in man, allow us to clearly distinguish that which is due to fashion or custom, from that which is deeply rooted in our heredity. To avoid repetition I refer my readers to Chapter VI, to examine the differences between heredity and custom.