Some animals share the properties of man and the quadrupeds, as the ape, the monkey, and the baboon. The monkey is a tailed ape. The baboon resembles the ape in form, only that it is bigger and stronger, more like a dog in face, and is more savage in its habits, and its teeth are more dog-like and more powerful.
Apes are hairy on the back in keeping with their quadrupedal nature, and they are hairy on the belly in keeping with their human form, for, as was said above, this characteristic is reversed in man and the quadruped--only that the hair is coarse, so that the ape is thickly coated both on the belly and on the back. Its face resembles man’s in many respects; in other words, it has similar nostrils and ears, and teeth like those of man, both front teeth and molars. Furthermore, whereas quadrupeds in general are not furnished with lashes on one of the two eyelids, this creature has them on both, only very thinly set, especially the under ones; in fact, they are very insignificant indeed. And we must bear in mind that all other quadrupeds have no under eyelash at all.
On its chest, the ape has two teats on two poorly developed breasts. It also has arms like man, except covered with much hair, and it bends its legs like man, with the convexities of both limbs facing one another. In addition, it has hands and fingers and nails like man, only that all of these parts are somewhat more beast-like in appearance. Its feet are exceptional in kind. That is, they are like large hands, and the toes are like fingers, with the middle one the longest of all, and the under part of the foot is like a hand except for its length, and stretches out towards the extremities like the palm of the hand. At the after end, this palm is unusually hard, and in a clumsy, obscure kind of way, it resembles a heel. The creature uses its feet either as hands or feet, and doubles them up as one doubles a fist. Its upper-arm and thigh are short in proportion to the forearm and the shin. It has no projecting navel, but only a hardness in the ordinary locality of the navel. Its upper part is much larger than its lower part, as is the case with quadrupeds; in fact, the proportion of the former to the latter is about five to three. Owing to this circumstance, and to its feet resembling hands and owing to its feet having heels and its toes having what is called a ‘palm,’ for these reasons, the animal is more often to be found on all fours than upright. It has neither hips, because it is a quadruped, nor a tail, because it is a biped, except for a tail as small as small can be, just a sort of an indication or a hint of one. The genitals of the female resemble those of the female in the human species; those of the male are more like those of a dog than like those of a man.
Aristotle (384–322 BC), Historia Animalium, Book II, Chapter 8.
Note: Aristotle had probably never seen an ape.