When two individuals of the same species cannot produce together, it is possibly occasioned by some slight difference of temperament, or accidental fault in the organs of generation. For two individuals of different species, to produce other individuals which do not resemble the one or the other in no fixed particular, and can consequently produce nothing like themselves, there needs but a certain degree of conformity between the forms of their bodies, and their organs of generation. But what an immense number of combinations are even necessary, even to suppose that two animals, male and female, of a certain species, have so much degenerated as to form a new species, and are no longer able to produce with any of their own kind but themselves! And also to suppose that the production of these two degenerated animals should follow exactly the same laws which are observed in the procreation of perfect animals; for a degenerated animal is itself a vitiated production, and how can a vitiated, depraved origin, become a new stock, and not only produce a constant succession of beings, but even to produce them in the same manner, and by following the same laws which reproduce animals, the origin of which are pure and uncorrupted?
Although we cannot demonstrate that the production of a new species, by degeneration, is a thing impossible in nature, yet the number of probabilities to the contrary render it incredible, for if some species have been produced by the degeneration of others, if that of the ass absolutely originated from the horse, it can only have happened by a succession of imperceptible degrees, and there must necessarily have been a greater number of intermediate animals, the first of which would have differed but slightly in its nature from the horse, and the latter would have approached by degrees to that of the ass. Upon the ground of this supposition we might ask, what is become of these intermediate beings? Why do we not see their representatives, their descendants? and why do the two extremes alone remain?
The ass is then an ass, and not a horse degenerated; a horse with a naked tail. The ass is neither a stranger, an intruder, nor a bastard; he has like all other animals, his family, his species, and his rank; his blood is pure and untainted, and although his race is less noble, yet it is equally good, equally ancient, with that of the horse. Why then is there so much contempt for an animal so good, so patient, so steady, and so useful? Do men despise, even among animals, those which serve them best and at the smallest expence? We educate the horse, take care of, instruct, and exercise him, whilst the ass is abandoned to the power of the lowest servant, or the tricks of children, so that instead of improving, he must lose by his education, and if he had not a fund of good qualities he would certainly lose them, by the manner in which he is treated. He is the sport of the rustics, who beat him with staffs, abuse, overload, and make him work beyond his strength. We do not consider that the ass would be in himself, and, with respect to us, the most beautiful, best-formed, and most distinguished of animals, if there were no horse in the world; he, however, holds the second instead of the first rank, and it is from that only he appears to be of no value. It is comparison alone degrades him; we look at, and give our opinions, not of himself, but comparatively with the horse. We forget that he is an ass, that he has all the qualities of his nature, all the gifts attached to his species, and only think of the figure and qualities of the horse which are wanting in him, and which he ought not to have.
He is naturally as humble, patient, and quiet, as the horse is proud, ardent, and impetuous; he suffers with constancy, and perhaps with courage, chastisement, and blows; he is moderate both as to the quantity and quality of his food; he is contented with the hardest and most disagreeable herbs, which the horse, and other animals, will leave with disdain; he is very delicate with respect to his water, for he will drink none but the clearest, and from rivulets which he is acquainted with; he drinks as moderately as he eats, and does not put his nose in the water through fear, as some say, of the shadow of his ears: as care is not taken to comb him, he frequently rolls on the grass, thistles, and in dust. Without regarding his road, he lies down and rolls as often as he can, and seemingly to reproach his master for the little care he takes of him, for he never wallows in the mud or in the water; he even fears to wet his feet, and will turn out of his road to avoid it; his legs are also drier and cleaner than those of the horse; he is susceptible of education, and some have been seen sufficiently disciplined for a public shew.
When young, they are sprightly, handsome, light and even graceful, but they soon lose those qualities either from age or bad treatment, and become slow, stubborn, and headstrong. The ass is ardent in nothing but love, or rather when under the influence of that passion he is so furious that nothing can retain him; he has been known to exhaust himself by excessive indulgence, and die some moments afterwards. As he loves with a kind of madness, he has also the strongest attachment to his progeny. Pliny assures us, that when they separate the mother from her young, she will go through fire to recover it. The ass is also strongly attached to his master, notwithstanding he is usually ill-treated; he will scent him at a distance, and distinguish him from all other men. He also knows the places where he has lived, and the ways which he has frequented. His eyes are good, and smell acute, especially with regard to females; his ears are excellent, which has also contributed to his being numbered among timid animals, who it is pretended have all long ears, and the hearing extremely delicate. When he is overloaded, he shews it by lowering his head and bending down his ears: when greatly abused, he opens his mouth and draws back his lips in a most disagreeable manner, which gives him an air of derision and scorn. If his eyes are covered, he remains motionless; and when he is laid down, and his head so fixed, that one eye rests on the ground and the other being covered with a piece of wood, he will remain in that situation without endeavouring to get up. He walks, trots, and gallops like the horse, but all his motions are smaller and much slower. He can however run with tolerable swiftness, but he can hold it only for a small space, and whatever pace he uses, if he is hard pressed, he is soon fatigued.
The horse neighs, but the ass brays; which he does by a long, disagreeable, and discordant cry, by alternative discords of sharp and flat. He seldom cries but when he is pressed by love or appetite. The she-ass has the voice clearer and more shrill; those that are gelded, bray very low, and though they seem to make the same efforts, and the same motions of the throat, yet their cry cannot be heard very far.
Of all the animals covered with hair, the ass is least subject to vermin, which apparently proceeds from the peculiar hardness and dryness of the skin, and for the same reason he is less sensible than the horse to the whip, and stinging of flies.