Whether coition is necessary for the generation of animals.
Above we discussed the disposition of all the members of animals," etc. In this fifth book one asks about generation, and first one asks about coition and propagation. First, whether coition is necessary for the generation of an animal.
1. It seems not. The generative power is bestowed upon every animal so that the species, which cannot be preserved in the animal itself, may be preserved in one like itself. Therefore, since this power is given to every animal, the animal does not require anything beyond this in order to generate.
2. Moreover, every animal is corruptible. Therefore, it needs something in the animal itself through which it can preserve its nature. Therefore, there exists a principle sufficient for generation in every animal per se.
The Philosopher says the opposite, and it is also apparent to the senses.
To this, one must reply that coition is necessary for the generation of some animals because the more perfect something is, the more things are required for its generation. Thus, for the generation of some imperfect animals a universal agent with properly disposed matter is sufficient, as is evident in the generation of those from putrefaction. But for the generation of perfect animals there is required an agent of the same species as well as a universal agent. But generation is of two types: one is the change of the whole into [another] whole, and in this way water is generated from fire. The other type of generation entails the separation of a part from the whole, and the generation of some animated things is like this. But in some animated things there exists only the active power of the one generating, and in others there exists only passive matter. And this is why, since every generation occurs from matter and from an agent, it is necessary that the two concur for the generation of ones like this. And this is why coition is necessary for the generation of ones like this.
1. On to the arguments. To the first, one must reply that the generative power is given to an animal for the sake of the preservation of the species. But this power can be understood in two ways: either as that which reproduces one like itself by itself (and this is not given to every animal) or as that which reproduces one like itself in another, and this can only occur by means of the contact of the male's penis with the woman's vulva, and this is why coition is necessary.
2. To the second argument one must reply that because every animal is corruptible, this is why it does not require something by which to preserve itself but instead requires something by which the species may be preserved in another, and this can occur by the propagation of the two [animals] and the action of one on the other through coition, by which a third animal is generated.
Whether coition is necessary for every animal.
One asks further whether coition is necessary for every animal.
1. And it seems so. For the operation of a nobler power is itself nobler. But an animal is nobler than a plant; therefore, the generative power is nobler in the animal than in the plant. But this would not be the case if generation did not occur differently in an animal than in a plant, and therefore, etc.
2. Moreover, a power does not lack an operation. But the operation of the vegetative power is to generate. Therefore, since the vegetative power is in every animal, each animal has a potential for generating. But this generation is present properly through coition with an animal, and therefore, etc.
The Philosopher implies the opposite in books four and five. For he says that the differentiation into male and female is not present in every animal, which would, however, be the case if this type of generation were suited to every animal.
One must reply that coition is not present in every animal, because the more perfect a thing is the more its perfection extends itself to many. But the operation of a perfect animal is to produce one like itself. But, according to Aristotle, every thing has been perfected when it can produce one like itself. But many animals are imperfect, and thus it is not surprising that they cannot produce ones like themselves. This is why they do not have the members that are properly designated for generation, but rather are produced by a universal agent, that is, by the sun, from mud or from putrefied matter.
1. On to the arguments. To the first, one must reply that a plant is more imperfect than an animal, and this is why fewer things are necessary for its generation. Thus the parts of a plant come to be from nutriment, over which the plant has power, and this is why if some parts are cut off from the plant they can be regenerated. But an animal is more perfect, and more things are required for its generation, and this is why the power that is in one like itself is not sufficient for the generation of a given animal in the same way that the power which is in each part of the plant is sufficient for the plant's generation.
2. To the second argument one must reply that wherever there is a power there is also the operation proper to the power. But the proper operation of the vegetative power is not to generate but to nourish and cause growth. Generation, however, is its proper operation only in the more perfect beings, and this is why, although every animal has a vegetative potency, nevertheless not every one can generate one like itself.
-  Although counterintuitive, this claim seems to refer to the possibility that one element will be entirely transmuted into another. In the background may also lie the belief that the fire of the Temple's altar was miraculously transformed into water and the water then back again into fire at 2 Mc 1.21-22. Indeed, Peter Damian remarks that "water is born of fire, and fire in turn is produced from water." See Ep. 153.52, trans. Blum and Resnick, Fathers of the Church, Mediaeval Continuation 7 (Washington, DC: The Catholic University of America Press, 2005), 44.