If we now turn to the two remaining species of personal affection—Friendship and Love—the emotional scenery undergoes a great change. In all the cases so far considered, blood-relationship was _a source of affection_; whereas in friendship it is commonly a disadvantage, and in Romantic Love it is positively abhorred, except in the more remote degrees. Some savage tribes, it is true, allow, or even prescribe, marriages between brother and sister—especially a younger sister; and cases occur of marriages between father and daughter, mother and son. But civilised society—guided by religious precepts, and possibly also by a vague instinctive recognition of the advantages of cross-fertilisation—condemns such unions as hideous crimes; and the mediæval theologians, in their extreme zeal, forbade all marriages within the seventh degree of relationship. In the case of friendship the objection to blood-relationship is not founded on a social or religious precept; but it exists all the same, as already noted. Perhaps Jean Paul’s maxim that friends may have everything in common except their room accounts for its existence. Brothers and sisters are commonly too much alike in their thoughts and tastes to become friends, in the special sense of the word. Hence it is that there is apt to be a deeper attachment between those brothers and sisters who have frequently been separated by school-terms than among those who are always together. For in friendship, as in love, a short absence is advantageous. Friendship is partly an outgrowth of the social instinct and partly a result of special associations, habit, community of interests and tastes. As a boy I had an opportunity to make some interesting observations on friendship among animals, showing that it differed in degree only, and not in kind or origin, from that of man. Among the animals we kept at our country-house were a dog, a pet sheep, and some pigs. The dog showed his confidence in the sheep’s amiable forbearance by abandoning his cold kennel on winter nights and seeking warmer quarters by the side of his woolly neighbour. For the pigs his friendly regards were shown in a less utilitarian manner, by driving away, unbidden and untaught, any swinish tramps that appeared, uninvited, to share their meals. But the most peculiar relations existed between the sheep and the pigs. In the absence of any other means of satisfying its gregarious or social instincts, the sheep joined the pigs every morning in their foraging expeditions in the woods, returning with them in the evening. And, what was still more remarkable, when after a time a dozen sheep were added to our stock of animals, the old pet remained faithful to the pigs, and paid no attention whatever to the newcomers. Here the friendly attachment, based on habitual association and the memory of mutual pleasures of grazing, was strong enough to overcome the inherited fellow-feeling for members of its own species.