In spite of all this, and as the result of custom and life in common, the individual sentiments of sympathy in man are easily extended to members of other races, especially as regards different sexes, so much so that enemies conquered and taken prisoners often became later on, owing to life in common, the friends or mates of their conquerors.
=Antipathy.=--Inversely, individual antipathies and enmity often occur not only between members of the same tribe but even between those of the same family. The latter may lead to parricide, fratricide, infanticide, or assassination of a conjoint.
=Phylogeny of Love.=--The social life of ants offers us some instructive analogies. In spite of the intense hostility of different colonies of ants among themselves, there may be obtained by habitude, often after many desperate combats, alliances between colonies which were hitherto enemies, even between colonies of different species. These alliances henceforth become permanent. This is very curious to observe at the time when the alliance begins to be formed. We then see certain individual hatreds persist, to a varying extent, for several days. Certain individuals of the weaker party are maltreated by other individuals of the conquering party. They cut off their limbs and antennæ and often martyrize them to death with a rabidness that sadly resembles human sentiments! Hatred and dispute between individuals of the same colony of ants are, on the other hand, extremely rare. I can guarantee the correctness of all these observations, having often repeated them myself and having recorded them in my works on the habits of ants. Moreover, they have since been confirmed by other writers.
After what we have just said, and especially if we take into consideration the numerous observations which have been made in biology, we can hardly doubt that the sentiment of sexual attraction, or the sexual appetite, has been the primary source of nearly all, if not all, the sentiments of sympathy and duty which have been developed in animals and especially in man. Many of these sentiments are no doubt little by little completely differentiated and rendered entirely independent of sexual sentiment, forming a series of corresponding conceptions adapted to divers social objects in the form of sentiments of amity. The latter in their turn have often become the generators of social formations and of a more generalized altruism. Many others, however, have remained more or less consciously associated with the sexual appetite, as is certainly the case in man.