Treatise of Human Nature/Book 2: Of the passions/Part 2/Section 12
Of the love and hatred of animals.
But to pass from the passions of love and hatred, and from their mixtures and compositions, as they appear in man, to the same affections, as they display themselves in brutes; we may observe, not only that love and hatred are common to the whole sensitive creation, but likewise that their causes, as above-explain'd, are of so simple a nature, that they may easily be suppos'd to operate on mere animals. There is no force of reflection or penetration requir'd. Every thing is conducted by springs and principles, which are not peculiar to man, or any one species of animals. The conclusion from this is obvious in favour of the foregoing system.
Love in animals, has not for its only object animals of the same species, but extends itself farther, and comprehends almost every sensible and thinking being. A dog naturally loves a man above his own species, and very commonly meets with a return of affection.
As animals are but little susceptible either of the pleasures or pains of the imagination, they can judge of objects only by the sensible good or evil, which they produce, and from that must regulate their affections towards them. Accordingly we find, that by benefits or injuries we produce their love or hatred; and that by feeding and cherishing any animal, we quickly acquire his affections; as by beating and abusing him we never fail to draw on us his enmity and ill-will.
Love in beasts is not caus'd so much by relation, as in our species; and that because their thoughts are not so active as to trace relations, except in very obvious instances. Yet 'tis easy to remark, that on some occasions it has a considerable influence upon them. Thus acquaintance, which has the same effect as relation, always produces love in animals either to men or to each other. For the same reason any likeness among them is the source of affection. An ox confin'd to a park with horses, will naturally join their company, if I may so speak, but always leaves it to enjoy that of his own species, where he has the choice of both.
The affection of parents to their young proceeds from a peculiar instinct in animals, as well as in our species.
'Tis evident, that sympathy, or the communication of passions, takes place among animals, no less than among men. Fear, anger, courage and other affections are frequently communicated from one animal to another, without their knowledge of that cause, which produc'd the original passion. Grief likewise is receiv'd by sympathy; and produces almost all the same consequences, and excites the same emotions as in our species. The howlings and lamentations of a dog produce a sensible concern in his fellows. And 'tis remarkable, that tho' almost all animals use in play the same member, and nearly the same action as in fighting; a lion, a tyger, a cat their paws; an ox his homs; a dog his teeth; a horse his heels: Yet they most carefully avoid harming their companion, even tho' they have nothing to fear from his resentment; which is an evident proof of the sense brutes have of each other's pain and pleasure.
Every one has observ'd how much more dogs are animated when they hunt in a pack, than when they pursue their game apart; and 'tis evident this can proceed from nothing but from sympathy. 'Tis also well known to hunters, that this effect follows in a greater degree, and even in too great a degree, where two packs, that are strangers to each other, are join'd together. We might, perhaps, be at a loss to explain this phænomenon, if we had not experience of a similar in ourselves.
Envy and malice are passions very remarkable in animals. They are perhaps more common than pity; as requiring less effort of thought and imagination.