How was the resemblance between apes and humans explained in pre-Darwinian biology? Who was the first biologist to note the resemblance?
Perhaps Aristole, as usual ...
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.
The ape [...] has also arms like man, only covered with hair, and it bends these 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 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; [...].
Book II.9 :
The monkey, as has been observed, is furnished with a tail. In all such creatures the internal organs are found under dissection to correspond to those of man.
But I've found no (attempted) explanation proposed by Aristotle.
I think that we have to consider the so-called "Ladder of Life" (or Great Chain of Being) system of classification of organisms as a sort of explanation.