Owing to its profoundly hereditary origin, this passion has a very instinctive character, and might quite as well have been mentioned in the preceding chapter. I deal with it here because it is naturally associated with other irradiations of the sexual appetite, and because it has a peculiarly mental character. =Relation Between Love and Sexual Appetite. Sympathy.=--Having entered the higher brain, or organ of mind, and become modified, complicated, and combined with the different branches of psychic activity, the sexual appetite takes the name of _love_, properly so-called. In order to better understand the relations of love to the sexual appetite we must refer to Chapter II. Let us begin with a short exposition of the phylogeny of the sentiments of sympathy, or the altruistic and social sentiments. In the lower animals with no separate sexes egoism reigns absolutely. Each individual eats as much as it wants, then divides, buds or conjugates, thus fulfilling the sole object of its existence. The same principle holds in the lower stages of reproduction by separate sexes. Spiders give us a good example. In these, copulation is a dangerous act for the male, for if he is not extremely careful he is devoured by the female, sometimes even before having attained his object, often soon afterward, in order that nothing may be lost. However, the female shows a certain consideration for her eggs, and sometimes even for the young after they are hatched. In higher stages of the animal kingdom sentiments of sympathy may be observed, derived from the sexual union of individuals. These are sentiments of attachment of the male for the female, and especially of the female (sometimes the male also) for their progeny. Such sentiments become developed and may be transformed into intense love between the sexes, of long duration. Birds, for instance, often remain faithful for many years, and even for life. From these simple facts is evolved the intimate relationship which exists between sexual love and other sentiments of sympathy, that is to say affection, or love in the more vague and more extended sense of the term.