Cats, dogs, and some I mean, birds, many species of mammals, they also have the sort of potential to show affection firstly because of the biological factor.
In descriptions of Nature one must seize on small details, grouping them so that when the reader closes his eyes he gets a picture. For instance, you'll have a moonlit night if you write that on the mill dam a piece of glass from a broken bottle glittered like a bright little star, and that the black shadow of a dog or a wolf rolled past like a ball.
And not only did he learn by experience, but instincts long dead became alive again. The domesticated generations fell from him. In vague ways he remembered back to the youth of the breed, to the time the wild dogs ranged in packs through the primeval forest and killed their meat as they ran it down.
Ay, in the catalogue ye go for men;
As hounds, and greyhounds, mongrels, spaniels, curs,
Shoughs, water-rugs, and demi-wolves, are 'clept
All by the name of dogs: the valued file
Distinguishes the swift, the slow, the subtle,
The housekeeper, the hunter, every one
According to the gift which bounteous nature
Hath in him closed.
He had learned well the law of club and fang, and he never forewent an advantage or drew back from a foe he had started on the way to Death. He had lessoned from Spitz, and from the chief fighting dogs of the police and mail, and knew there was no middle course. He must master or be mastered; while to show mercy was a weakness. mercy did not exist in the primordial life. It was misunderstood for fear, and such misunderstandings made for death. Kill or be killed, eat or be eaten, was the law; and this mandate, down out of the depths of Time, he obeyed.
Pessimists are just as illogical as optimists; insomuch as both envisage the aims of mankind as unified, and as having a direct relationship (either of frustration or of fulfilment) to the inevitable flow of terrestrial motivation and events. That is - both schools retain in a vestigial way the primitive concept of a conscious teleology - of a cosmos which gives a damn one way or the other about the especial wants and ultimate welfare of mosquitos, rats, lice, dogs, men, horses, pterodactyls, trees, fungi, dodos, or other forms of biological energy.
Zoologists seem to consider the cerebration of cats and dogs about 50-50 -- but my respect always goes to the cool, sure, impersonal, delicately poised feline who minds his business and never slobbers.