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 produced the original passion. Grief likewise is received 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 though almost all animals use in play the same member, and nearly the same action as in fighting; a lion, a tiger, a cat, their paws; an ox, his horns; a dog, his teeth; a horse, his heels: yet they most carefully avoid harming their companion, even though 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 observed 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 too packs that are strangers to each other are joined together. We might, perhaps, be at a loss to explain this phenomenon, 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.