Aristotle · a new plain-English translation from the original language
1| For this season is beneficial to their bodies. In others nothing of this sort is noticeably apparent, as with the sea-squirts. The particulars about these matters, and the places in which they occur, should be studied from the History.
2| Book IV. We have now spoken about the generation of animals, both in common and separately concerning them all. But since in the most perfect of them the female and the male are separated, and we say that these two capacities are principles for all things, both animals and plants, though some have them inseparable and others separate, we must speak first about the generation of these. For even while animals are still incomplete in their kind, the female and the male are already differentiated. But whether, even before the difference is evident to our perception, one is female and the other male — having taken on the difference in the mother, or earlier — is disputed. For some say that this opposition is present in the seeds straightaway, as Anaxagoras and other natural philosophers say; for they say the seed comes from the male, while the female provides the place, and that the male comes from the right-hand parts and the female from the left, and that in the womb the males are on the right and the females on the left. Others locate it in the womb, as Empedocles does; for he says that those that come into a warm womb become male, and those into a cold one female, and that the cause of the heat and cold is the flow of the menstrual discharge, whether it is colder or warmer, and older or more recent.
3| Democritus of Abdera says that the difference between female and male comes about in the womb, though not that one becomes female and the other male on account of heat and cold, but rather whichever seed prevails — the one that comes from the part in which male and female differ from each other. For Empedocles has really assumed this too carelessly, thinking that they differ from each other only in heat and cold, though he can see that the parts as a whole have a great difference — both the genitals and the womb. For if the animals were already molded, one having all the parts of the female, the other all the parts of the male, and then were placed into the womb as into a furnace, the one having a womb going into the warm place, the one not having one into the cold — then what has no womb would turn out female, and what has one would turn out male. But this is impossible. So on this point Democritus would speak better; for he seeks out the difference belonging to this generation and tries to state it. But whether he states it well or not is another matter. But indeed, even if heat and cold are the cause of the difference of these parts, this is what those who speak in that other way ought to have said.
4| For this is, so to speak, tantamount to speaking about the generation of male and female; for this plainly makes no small difference — the work of gathering, starting from that principle, the cause for the generation of these parts, so that it should follow of necessity that when the animal is chilled this part called the womb comes to be, but when it is heated it does not come to be. And in the same way concerning the parts that contribute to intercourse; for these too differ, as has been said before. Further, twins, female and male together, are often produced in the same part of the womb at the same time, and we have observed this adequately from dissections in all the live-bearing animals, both the land animals and the fish. Now if he had not observed this, he was reasonably mistaken in stating this cause; but if he had observed it, it is absurd still to think that the heat or cold of the womb is the cause. For both would have become either female or male, but as it is we do not see this happening. And to one who says that the parts of the offspring are torn apart (for he says that some are in the male and some in the female, and that this is why they desire intercourse with each other), it is necessary that the size of such things also be divided and that a union come about — but not on account of chilling or heating.
5| But about this sort of cause of the seed there would perhaps be much to say; for on the whole the manner of this causal account seems to be fanciful. But if the truth about seed is as we in fact have stated it — that it does not come from every part, and that what comes from the male does not provide any matter at all to the offspring — then the same answer must be given both to him and to Democritus, and to anyone else who happens to speak this way. For the body of the seed cannot be torn apart, part in the female and part in the male, as Empedocles says when he says, "but the nature of the limbs is torn apart, the one in the man's," nor can the whole be secreted from each, one part of it prevailing over another part so that the one becomes female and the other male. In general, to say that the prevailing excess of a part produces the female is better than to give no thought to the matter and blame heat alone — but it still requires an account of why the difference in the shape of the genitals happens at the same time, so that these things always follow together. For if it is because they are close together, then each of the remaining parts too ought to follow suit. For one part is near another among those that are winning out, so that the offspring would at once be both female and resemble the mother, or male and resemble the father.
6| Further, it is also absurd to suppose that only these parts come to be so, and that the body as a whole has not changed, and above all and first the veins, around which, as around an outline, the body of the flesh lies. It is not reasonable that these should have come to be of a certain quality on account of the womb, but rather the womb on account of them. For each of the two is a receptacle for a certain blood, but the veins come first. And the moving principle must always come first, and be the cause of generation by being of a certain quality. Now this difference between these parts as against one another does indeed occur in females and males, but it must not be thought to be a principle or a cause — rather there is another cause — even if no seed at all is secreted either from the female or from the male, but however it is that the seed which comes to be is constituted. And the same account applies also against those who say that the male comes from the right-hand parts and the female from the left, just as against Empedocles and against Democritus. For either the male contributes no matter at all, in which case those who speak this way would be saying nothing; or it does contribute, as they say, in which case the same answer must be given equally against the account of Empedocles too, who distinguishes female from male by the heat and cold of the womb.
7| Others do the same thing, defining by right and left, though they see that female and male differ even in whole parts. For what cause will there be why the body of the womb will belong to those coming from the left, but not belong to those coming from the right? For if it comes but this part does not take hold, there will be a female without a womb, and, as it happens, a male with one. Further, as has also been said before, a female has been observed on the right side of the womb and a male on the left, and both in the same side — and this not once but many times — or the male on the right side and the female on the left; and no less often both occur on the right side. Some people, persuaded of things much like these, likewise say that those who tie off the right testicle or the left, when they mate, come to produce males or females accordingly; for this is what Leophanes used to say. And concerning those who have one testicle removed by castration, some say the same thing happens, not speaking the truth but rather divining what will happen from what seems plausible, and assuming beforehand that it is so before actually seeing it come about that way — and moreover being ignorant that these parts contribute nothing at all to the production of male offspring or female offspring in animals.
8| A sign of this is that many animals are themselves both female and male, and produce some female and some male offspring, without having testicles, just as animals without feet do — for example the class of fishes and of snakes. Now, to suppose that heat and cold are the cause of male and female, and that the secretion comes from the right side or the left, has some reason to it; for the right side of the body is hotter than the left, and concocted semen is hotter, and what has coagulated is of this kind, and what has coagulated more is more generative. But to speak in this way is to grasp the cause from too far off; one must, so far as the available options allow, come as close as possible to the first causes. Now concerning the whole body and its parts, what each is and for what cause, this has been stated earlier elsewhere. But since male and female are distinguished by a certain capacity and incapacity (for that which is capable of concocting and forming and secreting semen possessing the principle of the form is male — by principle I mean not the sort of thing from which, as from matter, something comes to be such as the begetter is, but the first moving principle, whether it is able to do this in itself or in another —
9| while that which receives it but is unable to form and secrete it is female) — further, if all concoction is worked by heat, then among animals too the males must necessarily be hotter than the females. For on account of coldness and incapacity the female has more blood in certain places; and this is itself the opposite sign to the one on account of which some suppose the female to be hotter than the male, namely the discharge of the menses. For blood is hot, and what has more of it is hotter. They suppose that this condition comes about through an excess of blood and heat, as though all blood could equally count as blood so long as it is merely liquid and blood-colored, and as though it did not become both less in quantity and purer in well-nourished animals. And they suppose that, as with the residue in the belly, the greater amount rather than the lesser is a sign of a hotter nature. And yet the opposite is the case. For just as, in the working of crops, out of a great quantity of the first material only a little of the useful part is separated off, and in the end the final part is a small fraction of the original quantity, so too again in the body, as the parts take over the work in succession, the final product that comes from all the nourishment is altogether small.
10| This, in some animals, is blood, and in others what is analogous to it. Since the one is capable and the other incapable of secreting the residue pure, and every capacity has some organ — the same organ belonging both to the capacity that achieves the result worse and to the one that achieves it better — and since male and female are opposed in just this way ('capable' and 'incapable' being said in several ways), it is necessary that both female and male have organs: for the one, then, the organ is the womb, and for the other, the perineum. And nature assigns to each at the same time both the capacity and the organ; for it is better so. That is why each of these regions comes to be together with both the secretions and the capacities, just as sight does not come to be without eyes, nor is the eye completed without sight, and the belly and the bladder come to be together with the capacity to hold the residues. And since that from which each thing comes to be is the same as that from which it grows — and this is nourishment — each of the parts would come to be from that kind of matter of which it is receptive, and from that kind of residue. Further, again, as we say, it comes to be in a way out of its contrary. A third point, in addition to these, must be grasped: that if destruction is into the contrary, then what is not mastered by the formative agent must necessarily change into the contrary.
11| With these points laid down, it should now be clearer for what cause the one becomes female and the other male. For whenever the principle does not master the material, nor is able to concoct it on account of a deficiency of heat, nor bring it to its own proper form, but is defeated in this respect, it necessarily changes into the contrary. And the female is contrary to the male, precisely in respect of that by which the one is male and the other female. And since it differs in its capacity, it also has a different organ; so that it changes into that kind of organ. And when one critical part changes, the whole constitution of the animal differs greatly in form. One can see this in eunuchs, who, when a single part is mutilated, change so much from their original form that they come close to having the appearance of the female. The cause of this is that some parts are principles; and when a principle is disturbed, many of the things that follow from it must necessarily shift as well. If, then, the male is a certain principle and cause, and is male in respect of some capacity it has, while it is female in respect of an incapacity, and the boundary between the capacity and the incapacity is being able or not being able to concoct the final nourishment — which in blooded animals is called blood, and in the others what is analogous to it — and the cause of this lies in the principle, in the part that holds the principle of natural heat, then it is necessary that in blooded animals a heart forms, and that what comes to be will be either male or female.
12| In the other kinds, the female and the male belong to whatever is analogous to the heart. The principle of female and male, then, and this cause, lies here too. But an animal is already female or male when it also has the parts by which the female differs from the male. For it is not male or female in virtue of just any part whatever, any more than it sees or hears in virtue of just any part. Taking the matter up again, we say that semen has been posited as being the final residue of nourishment. By final I mean what is carried to each part. That is also why the offspring resembles the parent. For it makes no difference whether it is said to come away from each of the parts or to be added to each part, though the latter is the more correct way of putting it. The semen of the male differs in that it has within itself a principle of such a kind as to set in motion, even within the animal itself, and to concoct through to the final nourishment, whereas that of the female provides only matter. If it masters the matter, then, it brings it over into itself, but if it is mastered, it changes into its contrary, or into destruction. And the female is the contrary of the male. It is female by the lack of concoction and the coldness of its blood-like nourishment. And nature assigns to each of the residues its receptive part.
13| Semen is a residue. In the hotter and male blooded animals this is of moderate bulk in amount, which is why the receptive parts in males are ducts for this residue. In females, on account of lack of concoction, there is a bulk of blood-like matter (for it is unworked), so that some receptive part is also necessary, and that this be unlike the male's duct and have some size. That is why the nature of the womb is of this kind. And it is in this part that the female differs from the male.
14| For what cause, then, one becomes female and the other male has been stated. And what actually happens provides evidence for what has been said. For young animals produce more females than those in their prime do, and so do aging animals; for in the former the heat is not yet complete, while in the latter it is failing. And bodies that are more moist and more feminine produce more females, and so does moist semen more than semen that has coagulated; for all these things happen on account of a deficiency of natural heat. And it is evidence that north winds produce more males than south winds do; hence such offspring are also fuller of residue. And the greater residue is harder to concoct; that is why in males the semen is then more liquid, and in women the discharge of the menses is greater. And the fact that the natural menses occur more as the months wane happens for the same cause. For this period of the month is colder and moister, on account of the waning and disappearance of the moon; for the sun produces winter and summer over the whole year, while the moon does so within the month. And this happens not on account of solstices, but the one condition occurs while the light is waxing, the other while it is waning. And herdsmen say that it makes a difference for the production of females and males not only whether the mating happens to occur in north or south winds, but also whether the animals, while mating, look toward the south or the north;
15| So it is that sometimes a small tilt becomes the cause of coldness and heat, and these in turn the cause of generation. Now the female and the male are, on the whole, opposed to each other with respect to the generation of males and the generation of females, for the causes already stated; nonetheless, there must also be a due proportion between them, for everything that comes to be, whether by craft or by nature, comes to be in accordance with some ratio. Heat, when it is too dominant, dries up the moist matter, and when it falls far short, it fails to bring it together; rather, in relation to what is being fashioned, it must have the ratio of the mean. If not, then just as in the case of things being boiled, too much fire scorches while too little fails to cook, and in both cases the result is that the thing coming to be is not brought to completion, so too in the mixture of male and female there must be due proportion. And this is why it happens that many men and many women fail to produce offspring with each other but do produce offspring once separated and paired with others, and why these contrarieties occur sometimes when they are young and sometimes when they are older, alike with respect to fertility and infertility and the generation of males and of females. And region differs from region, and water from water, with respect to these things, for the same causes; for the food that results is of a certain quality, and so is the condition of the body, on account of the mixture of the surrounding air and of what is taken in, but above all on account of the nourishment supplied by water,
16| for this is what is taken in in the greatest quantity, and it is nourishment in all cases, even in dry foods. This is why hard and cold waters cause childlessness in some cases and the birth of females in others. The same causes also explain why some offspring come to resemble those who bore them and others do not, some resembling the father and others the mother, both with respect to the whole body and with respect to each part, and why they resemble their own parents more than their more remote ancestors, and these ancestors more than chance persons, and why males resemble the father more and females the mother, while others resemble none of their kin, yet still resemble some human being, and others do not even resemble a human being in shape but are already a monstrosity. For even one who does not resemble his parents is already, in a way, a kind of monstrosity, for in such cases nature has in a way departed from the genus. Now the first principle at work is that the offspring should become female rather than male. But this is a necessity imposed by nature, for the class of things divided into female and male must be preserved. Since it is possible for the male principle sometimes to fail to gain mastery, either on account of youth or old age or some other such cause, it is necessary that the generation of females should occur among animals. But the monstrosity is not necessary with a view to the end and the cause that is for the sake of something, but is necessary in the sense of being accidental, since this is the point from which its origin must be understood.
17| For when the residue in the menstrual fluid, the spermatic residue, is well concocted, the motion deriving from the male will produce the shape entirely on its own terms. For it makes no difference whether one speaks of the seed or of the motion that causes each of the parts to grow, nor whether one speaks of the motion that causes growth or the motion that constitutes the parts from the start, for the account of the motion is the same in either case. So then, if this motion prevails, it will produce a male and not a female, and one resembling the begetter and not the mother; but if it fails to prevail, then with respect to whatever capacity it fails to prevail in, it produces the deficiency corresponding to that capacity. I mean the following by each capacity. The begetter is not only male but a male of a certain kind, for instance Coriscus or Socrates, and he is not only Coriscus but also a human being. And in this way some characteristics belong to the begetter more closely and others more remotely, in virtue of his being a begetter, and not accidentally, as would be the case if the begetter happened to be literate or someone's neighbor; and for the purpose of generation, what is proper and particular to him always has more force. For Coriscus is both a human being and an animal, but he is closer to what is proper to him as human being than as animal. Both the particular individual and the genus beget, but the particular individual does so more,
18| for this is the substance. For what comes to be, comes to be a thing of a certain quality, but it is a this-something, and this-something is the substance. This is why the motions present in the seeds of all such things derive from the capacities, but potentially they also derive from the ancestors, and more so, always, from whichever of the particular individuals is closer. By the particular individuals I mean Coriscus and Socrates. Now since everything that departs from its state departs not to any chance state but to its opposite, that which is not mastered in the process of generation must necessarily depart and become the opposite, in respect of whatever capacity the begetter and mover failed to master. If, then, it is qua male that it fails, the offspring becomes female; but if it is qua Coriscus or Socrates that it fails, the offspring comes to resemble not the father but the mother, for the mother is opposed to the father as a whole, just as the particular female begetter is opposed to the particular male begetter. And the same holds with respect to the capacities next in line, for the transition is always rather to the next in the line of ancestors, both on the father's side and on the mother's. Some of the motions are present as actuality and others as potentiality: as actuality, the motions belonging to the begetter and to the universals, such as human being and animal; as potentiality, the motions belonging to the female and to the ancestors.
19| It changes, then, by departing toward the opposites, but the motions that do the fashioning, when they are dissolved, resolve into the ones nearest to them; for instance, if the motion of the begetter is dissolved, it passes over, by the smallest difference, into the motion of the father, and secondly into that of the grandfather; and in the same way, both among males and among females, the motion of the female begetter passes into that of the mother, and if not into that, into that of the grandmother; and likewise for those further up the line. Now it is most natural, qua male and qua father, for mastery and being mastered to occur together, for the difference is small, so that it is no great matter for both to occur at once, since Socrates is a man of a certain kind. This is why, for the most part, males resemble the father and females the mother. For the departure occurs in both respects at once, and the female is opposed to the male, and the mother to the father, and departure is toward the opposites. But if the motion deriving from the male masters while the motion deriving from Socrates does not, or the reverse, then it happens that males come to resemble the mother and females the father.
20| And if the motions are dissolved, and the offspring remains male, but the motion of Socrates is dissolved into that of the father, the male offspring will resemble the grandfather, or some other of the more remote ancestors, according to this same account. But if it is mastered qua male, the offspring will be female, resembling above all the mother; and if this motion too is dissolved, the resemblance will be to the mother's mother, or to some other ancestor further up the line, according to the same account. The same manner of explanation applies also to the parts of the body, for of the parts too, some often resemble the father, others the mother, and others some of the ancestors; for of the parts also, some motions are present as actuality and others as potentiality, as has often been said. In general one must grasp these underlying assumptions: one, the one already stated, that of the motions some are present as potentiality and others as actuality; and two others, that what is mastered departs toward the opposite, while what is dissolved passes into the motion next to it, and passes less into the nearer one when the dissolving is slighter, and more into the more remote one when it is greater. In the end things become so blended together that the offspring resembles none of its own kin and relations, but only what is common is left, and it is simply a human being.
21| The cause of this is that this attaches to all particulars: for man is universal, but Socrates, the father, and the mother, whoever she was, belong to particulars. The cause of the motions being undone is that the agent is also acted on by the patient: for example, the cutting thing is blunted by what is cut, and the heating thing is cooled by what is heated, and in general whatever moves something, apart from the first mover, is moved back by some counter-motion — for example, what pushes is in turn pushed back somewhat, and what presses is pressed back. And sometimes it is acted on more than it acts altogether: the heating thing is cooled and the cooling thing is heated, at times doing nothing at all, at times doing less than it suffers. This has been discussed in the works that determine acting and being acted on, as to which existing things admit of acting and being acted on. The thing acted on departs from its course and is not mastered either through a deficiency in the power of the agent that concocts and moves it, or through the quantity and coldness of the thing being concocted and differentiated. For mastering it in one respect but not in another makes what is being formed take on many shapes, as happens with athletes because of their heavy eating. For because their nature is unable to master the quantity of food, so as to grow proportionately and keep the same shape, the parts become different — and sometimes so much so that they resemble their former selves not at all.
22| Similar to this is also the disease called satyriasis: for in this case too, because of a quantity of unconcocted discharge or breath falling in upon the parts of the face, the animal's face comes to look like a satyr's. As to the cause, then, why females and males come to be, and why some offspring resemble their parents — females resembling females and males resembling males — while others are the reverse, females resembling the father and males the mother, and in general why some resemble their ancestors and others resemble none of them, both as regards the whole body and each of the parts — all this has been determined. Some of the natural philosophers, and others too, have spoken about these matters, about the cause why offspring come to be like and unlike their parents. They state the cause in two ways. For some say that, from whichever parent more seed comes, the offspring resembles that one more, the whole resembling the whole and part resembling part in like manner, on the ground that seed departs from each of the parts; and if an equal amount comes from each, the offspring resembles neither. But if this is false, and seed does not depart from every part, then it is clear that what has been said could not be the cause of resemblance and unresemblance either.
23| Further, they cannot easily explain how it can happen at the same time that a female offspring resembles the father and a male offspring resembles the mother. For those who, like Empedocles or Democritus, give the cause of female and male in another way, say things that are impossible. And those who say that female and male come to be through more or less coming from the male or the female, and that this is why one offspring is female and another male, would not be able to demonstrate how the female is to resemble the father and the male the mother; for it is impossible for more to come from both at the same time. Again, what is the cause why offspring commonly resemble ancestors, even remote ones? For no seed at all has come from those ancestors. Rather, those who state the remaining account of resemblance speak better both on the other points and on this one. For there are some who say that the seed, though one, is a kind of assemblage of many seeds. Just as, if someone were to mix many flavors into one liquid, and then draw a portion from it, he could draw not always an equal amount from each ingredient, but sometimes more of this one, sometimes more of that one, and sometimes some of one and none at all of another — this, they say, happens also with the seed, since it is a mixture of many things.
24| For from whichever of the parents the greatest portion is present, the offspring's form comes to resemble that one. This account is unclear and fanciful in many respects, but it also wants to say something better, namely that this exists not in actuality but in potentiality, which is what it calls the 'assemblage of many seeds.' For in the former way it is impossible, but in this way it is possible. Nor is it easy, giving a single account of the cause, to state the causes for everything at once: for the coming to be of female and male, and why the female is often like the father and the male like the mother, and again the resemblance to ancestors, and further the cause why sometimes the offspring is a human being but resembles none of these, and sometimes, proceeding in this way to the end, what is produced turns out not even to be a human being but only some kind of animal — the things which are in fact called monstrosities. For it also follows from what has been said to state the causes concerning such things. For in the end, when the motions are being undone and the matter is not mastered, what remains is above all the universal, and this is 'the animal.' They say the creature produced has the head of a ram or of an ox, and likewise in other cases the head of some other animal — a calf with a child's head, or a sheep with an ox's head.
25| All these things happen because of the causes already stated, but none of them is actually what people say, they are only similar to it. This happens even in creatures that are not deformed at all, which is why jokers often liken some who are not good-looking to a goat blowing fire, or a ram butting. And a certain physiognomist reduced all faces to the appearances of two or three animals, and often persuaded people by what he said. That it is impossible for such a monstrosity to occur, one animal within another, is shown by the periods of gestation, which differ greatly between man and sheep and dog and ox; and it is impossible for each to be produced except according to its own proper time. Some monstrosities, then, are spoken of in this way; others are so called because they have a form with too many parts, being produced with many feet and many heads. The accounts of the cause are closely related, and in a way similar, both for monstrosities and for maimed animals.
26| For a monstrosity too is a kind of deformity. Democritus, then, said that monstrosities come about because two seeds fall, one setting out earlier and the other later, and that the later one, coming out, enters the womb so that the parts grow together and overlap. And since in birds mating happens quickly, he says that their eggs and their coloring always overlap as a result. But if it happens that several offspring are produced from a single seed and a single mating, which is evidently the case, it is better not to go the long way round, passing over the short one. For it is most necessary for this to happen in just such cases, whenever the seeds are not kept separate but come together at the same time. If, then, one must locate the cause in the seed from the male, it should be stated in this way. But in general one should rather suppose the cause to lie in the matter and in the embryos as they are being formed. That is why such monstrosities occur very rarely among animals that bear a single offspring, but more often among those that bear many, and most of all among birds, and among birds most of all in hens. For hens produce many offspring, not only by laying often, as the pigeon family does, but also by having many embryos at once and by mating at every season.
27| This is also why they often produce twins: for the embryos grow together because they are close to one another, just as sometimes happens with a number of fruits growing together. Among these, whenever the yolks are separated by the membrane, two chicks are formed, distinct from each other, having nothing abnormal about them; but whenever they are continuous and nothing divides them, the chicks that come from these are monstrous, having one body and one head but four legs and wings, because the upper parts are formed from the white and are formed earlier, the nourishment for them being dispensed from the yolk, while the lower part comes later, and the nourishment is one and undivided. Already, too, a two-headed snake has been observed, for the same reason; for this kind also lays eggs and produces many at a time. But the monstrous is rarer among snakes because of the shape of the uterus: the mass of eggs is arranged in a row because of its length. And among bees and wasps nothing of this sort occurs, for their brood is laid in separate cells. But among hens the opposite is the case, and from this too it is clear that one must suppose the cause of such things lies in the matter; for indeed this happens more, among the other animals too, in those that produce many young at a birth.
28| This is why it happens less in the human being: for the human, for the most part, produces one offspring at a birth and produces it fully formed, since even among human beings, in whatever places women bear many at a birth — as around Egypt — this occurs more often. Among goats and sheep it occurs more, for these produce many young. And still more among the many-toed animals; for such animals produce many young and do not produce them fully formed, as with the dog: for a dog bears most of its young blind. But the cause for which this occurs, and the cause for which these animals produce many young, must be stated later. But nature has already paved the way toward producing monstrosities in the fact that these animals do not generate offspring like themselves, on account of their incompleteness; and the monstrous, too, belongs among things unlike their parents. This is why this occurrence attaches itself especially to the nature of such animals. For it is especially among these that the so-called "between-litters" occur. These are creatures that have suffered something monstrous in some respect; for a lack or an excess of some part is monstrous. For the monstrous is one of the things contrary to nature — not contrary to nature as a whole, but to nature as it holds for the most part; for concerning what is always and what is of necessity, nothing occurs contrary to nature, but among things that occur in one way for the most part, while admitting also of occurring otherwise — since even among these, in as many cases as depart from this normal order, yet do so always and not by chance, the thing seems less a monstrosity, because what is contrary to nature is in a certain way also in accordance with nature, whenever the nature according to form fails to master the nature according to matter.
29| This is why people do not call such things monstrosities, nor do they in the other cases where something regularly occurs, as with fruits. For instance there is a vine that some call the "smoke-vine": if it bears black clusters, they do not judge this a monstrosity, because this vine is accustomed to do this quite often. The cause is that it is by nature intermediate between the white and the black variety, so that the change is not a great remove, nor, as it were, contrary to nature; for it does not pass into another nature altogether. Among animals that produce many young the same thing occurs, and moreover, because of the multiplicity of the litter, the young hinder one another's completion and their generative motions. Now concerning the multiplicity of offspring and the excess of parts, and the paucity or singleness of offspring and the deficiency of parts, one might raise a difficulty. For sometimes some are born having more fingers, others only one, and similarly with the other parts: for there occurs both excess and stunting, and some are even born having two sets of genitals, one male and one female, both among human beings and especially among goats. For there occur what are called "she-goat-bucks" because they have both female and male genitals; and there has already occurred a goat that had a horn growing at its leg.
30| Changes and defects also occur with regard to the internal parts, in that some animals lack certain of them, or have them stunted, or have more than the normal number, or have them displaced in position. No animal has ever been born without a heart; but some are born without a spleen, some with two, and some with only one kidney; none is born without a liver at all, though some are born without the whole of it. All these cases occur among animals that have reached completion and are alive. Animals are also found lacking gall, though naturally suited to have it; and others have more than one gall-bladder. There have already occurred cases of displacement in position too, the liver being on the left and the spleen on the right. Now these cases have been observed in animals that have reached completion, as has been said; but among animals still being born there is much confusion of every kind. Those that depart from the normal nature only slightly are generally found to live, while those that depart more do not live, whenever what is contrary to nature affects the parts that control life. The inquiry concerning these matters is whether one must suppose the same cause for the singleness of offspring and the deficiency of parts, and for the excess and the multiplicity of offspring, or not the same cause. First, then, why some animals produce many young and others only one — this is a question one might reasonably find surprising.
31| For the largest animals produce only one offspring at a birth — for example the elephant, the camel, the horse, and the solid-hoofed animals generally; and of these, some are larger than the rest, and some differ greatly from the others in size. The dog and the wolf and all the many-toed animals produce many young, nearly without exception, and so do the small ones among these, for instance the mouse kind. The cloven-hoofed animals produce few young, except the pig; the pig belongs among those that produce many. For it stands to reason that the large animals should be able to generate more and to carry more seed. But the very thing that causes the wonder is the cause of there being nothing to wonder at: it is precisely because of their size that they do not produce many young; for in such animals the nourishment is used up for the growth of the body. But from the smaller animals nature, taking away from their size, adds the surplus to the seminal residue. Further, the seed produced by the larger animal must necessarily be more in quantity, and that of the smaller animals less. Now it is possible for many small young to come to be in the same womb at once, but many large ones is difficult; and to animals of middling size nature has assigned the middling number. We have already stated earlier the cause why some animals are large, others smaller, and others of middling size.
32| Among animals, some produce only one offspring, some few, and some many, and for the most part the solid-hoofed animals produce one, the cloven-hoofed produce few, and the many-toed produce many. The cause of this is that, for the most part, size is determined along these same lines of difference. This is not, however, the case with all of them without exception: for the cause of producing few or many young is the largeness or smallness of the bodies, not the fact of the kind being solid-hoofed, many-toed, or cloven-hoofed. Here is evidence of this: the elephant is the largest of animals, yet it is many-toed; and the camel, though cloven-hoofed, is the largest of the rest. And not only among land animals but also among winged and swimming creatures, the large ones produce few young and the small ones many, for the same cause. Likewise too among plants, it is not the largest that bear the most fruit. We have now stated, then, why some animals are by nature prolific and others produce few young. But one might be more surprised at the difficulty just mentioned in the case of the animals that produce many young, since it appears that such animals often become pregnant with many from a single mating; and — whether the male's seed contributes to the matter by becoming a part of the embryo and being mixed with the female's seed, or whether it does not do so in this way, but rather, as we say, gathers together and forms the matter present in the female — the seminal residue acting the way rennet acts on the fluidity of milk — for what cause, in either case, does it not produce a single animal of large size instead of many small ones?
33| Just as there the sap does not separate out by forming some fixed amount, but the more of it there is, the greater the curdled mass becomes, so too here: to say that the regions of the uterus draw the seed, and that this is why more offspring come to be, on account of the number of the regions and because the cotyledons are not one, is not a unified account. For often two offspring come to be in the same region of the uterus, while in animals that bear many young, once it is filled with embryos, they are seen lying in a row. This is clear from dissections. But just as, when animals reach their full growth, each has some size that admits of a greater and a lesser degree—sizes than which it could become neither greater nor smaller, but within the intervening range of size they take on excess and deficiency relative to one another, and so one man becomes bigger and another smaller, and likewise with any of the other animals—so too the seminal matter out of which an animal comes to be is not unlimited in either direction, greater or smaller, such that it could come to be out of any quantity whatever. So then, whichever animals emit more residue than what suffices for the origination of a single animal, for the reason stated, it is not possible for a single animal to come to be from the whole of it, but only as many as are marked off by the sizes that are reached.
34| Nor does the seed of the male, or the power in the seed, put together anything more or less than what its nature allows. Likewise, if the male emits more seed, or more powers within the seed when it is divided, the greater amount will not produce anything bigger—rather the opposite, it will destroy it by drying it out. For fire, too, does not heat water more the more of it there is; rather there is a limit to the heat, and once that limit is reached, if one increases the fire further, the water no longer becomes hotter, but evaporates more, and in the end disappears and becomes dry. Since, then, it appears that the residue of the female and that from the male need a certain proportion relative to one another, those of the males that emit seed—the animals that bear many young at once emit, on the one hand, male seed capable, when divided up, of forming several offspring, and, on the other hand, so much female matter that several formations come to be. The example given about milk is not a parallel case: for the heat of the seed forms not only a certain quantity but also a certain quality, whereas the heat in the sap and in rennet forms only the quantity. So then, this is itself the cause of many fetuses coming to be, rather than one continuous whole out of all of it, in animals that bear many young: that a fetus does not come to be out of just any quantity whatever, but if it is too little, there will be none, and likewise if it is too much;
35| for the power both of what is acted upon and of the heat that acts is fixed within limits. Likewise too, in animals that bear a single offspring and are large, many offspring do not come to be out of a large quantity of residue; for in those animals too, a fixed quantity produces a fixed quantity. So then, such an animal does not emit more of this matter, for the reason already stated; but whatever it does emit is, by nature, just enough that a single fetus comes to be from it. But if on some occasion more comes, it then bears twins. This is why such cases are thought to be rather monstrous, because they occur contrary to what happens in most cases, and to what is usual. Man, however, straddles all the kinds: for he sometimes bears one, sometimes many, and sometimes few, though by nature he is most a bearer of a single offspring; on account of the moistness and heat of his body he is a bearer of many (for the nature of seed is moist and hot), but on account of his size he is a bearer of few, or of one. And on account of this it has come about that man alone among animals has irregular periods of gestation. For the other animals have a single fixed time, but human beings have several: for children are born at seven months and at ten months, and at the times in between;
36| for even eight-month children live, though less often. One might grasp the cause of this from what has just been said, and it has been discussed in the Problems. Let this, then, be settled in this manner concerning these matters. As for parts that are in excess contrary to nature, the same cause accounts also for the bearing of twins. For the cause already operates at the level of the fetuses, if the fetus forms more matter than accords with the nature of the part. For then it comes about that one part is bigger than the others—a finger, say, or a hand or a foot or one of the other extremities or limbs—or, if the fetus is split apart, that several come to be, just as eddies do in rivers. For in rivers too, when the moving current, carried along and possessing motion, meets an obstruction, two formations come to be out of one, each possessing the same motion; and the same thing happens in the case of fetuses. They grow together mostly close to one another, but sometimes also at a distance, on account of the motion that occurs in the fetus—and above all because the excess of matter, from wherever it was taken away, is restored there, while the form belongs where the excess occurred. Whenever it happens that such creatures have two sets of genitals, one male and one female, of the excess parts one is always dominant and the other non-functional, since it is always weakened as regards nourishment, being contrary to nature, but it does grow attached, the way tumors do;
37| for these too take on nourishment, even though they arise later and are contrary to nature. And it comes about that if the formative agent prevails on both sides, two similar offspring result, and if it is overpowered on both sides, likewise two similar offspring; but if it prevails on one side and is overpowered on the other, one is female and one is male. For it makes no difference whether one states this cause, on account of which the one comes to be female and the other male, in application to the parts or to the whole. And in cases where such parts come to be deficient, such as some extremity or other limb, the cause must be thought the same, for it is a similar case, even where the offspring is aborted altogether. Many abortions of fetuses do occur. Now supplementary growths differ from twin-bearing in the manner stated, and monstrosities differ from these in that a number of them are grown together as one. And some cases occur in this way too, when it happens in connection with the larger and more governing parts—for instance some creatures have two spleens and several kidneys. Further, there are shiftings of parts when the motions are diverted and the matter shifts its place. Whether the monstrous animal is to be reckoned one, or several grown together, must be judged by reference to the governing principle: for example, if the heart is such a part, then a creature having one heart is one animal, while the parts in excess are supplementary growths, but creatures having several hearts are to be reckoned as several, though grown together on account of the joining of the fetuses.
38| It happens often, too, in the case of animals not thought to be defective, that in many that have already reached maturity some of the passages have grown together while others have grown awry. For in some females the mouth of the uterus has actually remained grown shut, and then, once the season for the menses has come and pains set in, in some cases it has burst open of itself, in others it has been opened by physicians; and in some cases it has turned out that the woman was destroyed, either because the rupture occurred by force or because it could not occur. And in some boys the opening of the genitals and the passage by which the residue from the bladder passes out do not coincide at the same point, but the latter lies lower down; this is why they urinate sitting down, and, since their testicles are drawn up high, they appear to those observing from a distance to have both a female and a male organ at once. There have also been cases where the passage for solid food has grown shut in certain animals, both in sheep and in others, since there was even an ox at Perinthus through which the food, strained fine, passed out by way of the bladder; and when the anus was cut open it quickly grew together again, and those who kept cutting it open could not get the better of it.
39| We have discussed few offspring and many offspring, and the outgrowth of parts that are in excess or deficient, and further the monstrous births. Of animals, some do not superfetate at all, others do; and of those that superfetate, some are able to rear the fetuses further, others sometimes can and sometimes cannot. The cause of not superfetating is that they bear one at a time. For the solid-hooved animals do not superfetate, nor do those larger than these; for because of their size the residue is used up entirely into the fetus. For all these have bodily size, and in the large animals the embryos too are correspondingly large; this is why the elephant's embryo is as large as a calf. Animals that bear many at a time superfetate because what is more than one is, for each, a superfetation upon the other. Of these, whichever have size, as man does, if the second mating comes close upon the first, the animal rears the superfetated offspring too; for such a thing has actually been observed to happen. The cause is what has been stated: for even in a single act of intercourse more semen comes out than is needed, and this, when divided, produces multiple births, of which one lags behind the other. But when the mating happens to occur once the fetus has already grown, superfetation sometimes occurs, though rarely, because the womb closes up, as it does for the most part in women once they are pregnant, right up to the time of delivery.
40| But if it should ever happen (for this too has already occurred), the animal cannot bring it to completion, but fetuses fall away resembling what are called miscarriages. For just as in the single-bearing animals, because of their size, all the residue is diverted into the pre-existing fetus, so it is with these too, except that in the former case this happens at once, in the latter only once the embryo has grown; for at that point they are in a condition similar to the single-bearing animals. Likewise, because man is by nature multiparous, and there is something left over both in the size of the womb and in the residue, though not so much as to rear a second offspring to term, woman and the mare are the only animals that admit mating while already pregnant — the woman for the reason stated, the mare both because of the hardness of her nature and because there is something left over in the size of the womb, more than for one, but less than enough for another to be brought to completion by superfetation. And the mare is by nature given to sexual desire because she is affected in the same way as hard-natured animals are; for those are as they are because no purgation occurs in them (this being for them what intercourse is for the males), and mares among females least of all discharge a purgation. In all live-bearing animals the hard-natured females are given to sexual desire, because they are in a condition similar to the males, namely that the semen has collected but is not being separated off.
41| For in females the purgation of the menses is an exit of semen; for the menses are unconcocted semen, as has been said before. This is why, among women, those who are intemperate in this kind of intercourse, when they bear many children, cease from their excitement; for once the seminal residue has been secreted out, it no longer produces desire for this intercourse. Among birds, the females are less given to sexual desire than the males, because they have their wombs near the diaphragm, whereas with the males it is the opposite; for they have their testicles drawn up inside, so that if the kind of such birds is by nature seminal, they always need this intercourse. So it happens that, in preparation for mating, in females the womb descends downward, and in males the testicles are drawn up. The cause, then, why some animals do not superfetate at all, while others do superfetate but sometimes rear the fetuses further and sometimes not, and the cause why some of these are given to sexual desire and others not, has been stated. Some of the animals that superfetate can rear the fetuses further even when a long interval separates the matings — namely, those whose kind is seminal, whose body does not have size, and which are multiparous.
42| For because they are multiparous they have roominess in the womb, and because they are seminal they discharge much residue in the purgation; and because their body does not have size, but the purgation exceeds by a greater ratio the nourishment needed for the fetus, animals can be formed even later and these too can be reared. Further, the wombs of such animals do not close up, because there is residue of the purgation left over. This has actually happened in the case of women too; for some pregnant women have purgation even throughout. But for them this is contrary to nature (which is why it harms the fetus), whereas for such animals it is in accordance with nature; for their body is constituted this way from the start, as is the hare's. For this animal superfetates; for it is not among the large animals, and it is multiparous (for it is many-toed, and many-toed animals are multiparous), and it is seminal. Its shagginess makes this clear; for it exceeds in the quantity of its hair, and indeed it is the only animal that has hairs under its feet and inside its jaws. Shagginess is a sign of an abundance of residue, which is why among men the hairy are more given to sexual desire and more full of semen than the smooth. The hare, then, often has some of its fetuses incomplete, while it brings forth others of its offspring fully completed.
43| Of the live-bearing animals, some bring forth incomplete animals, others complete ones: the solid-hooved and the cloven-hooved bring forth complete ones, while among the many-toed many bring forth incomplete ones. The cause of this is that the solid-hooved bear one at a time, while the cloven-hooved bear either one or, for the most part, two, and it is easy to rear a small number. Of the many-toed animals, all that bear incomplete young are multiparous; this is why, while the fetuses are still young, the mother can go on rearing them, but once they have grown and taken on size, since the body is no longer able to rear them, she brings them forth, just as the worm-bearing animals do. For of these too, some produce young that are almost entirely unarticulated, as the fox, the bear, and the lion do, and some of the others do similarly; and almost all are born blind, such as these and also the dog, the wolf, and the jackal. The pig alone, though multiparous, bears its young complete, and it alone straddles both categories; for it is multiparous like the many-toed animals, yet it is both cloven-hooved and solid-hooved — for there are, in fact, solid-hooved pigs somewhere. It is multiparous because the nourishment that would go to size is diverted into the seminal residue; for as a solid-hooved animal it does not have this size. And at the same time, as though disputing the nature of the solid-hooved, it is all the more cloven-hooved.
44| It is for this reason, then, that most pigs bear one, or two, or many at a time, but rear them to completion because of the good feeding condition of the body; for the body is like rich soil for plants, having sufficient and abundant nourishment. Some birds also bring forth young that are incomplete and blind, namely those among them that are multiparous without having bodily size, such as the crow, the jay, sparrows, and swallows; and also among the animals that bear few, those that do not bring forth abundant nourishment along with their young, such as the wood-pigeon, the turtle-dove, and the pigeon. And this is why, if someone pierces out the eyes of swallows while they are still young, they heal again; for while the eyes are still in process of forming, and not yet fully formed, they are destroyed, and so they grow and sprout afresh from the beginning. In general, incompleteness in birth comes about because of the inability to rear the young further, and the young turn out incomplete because of this earliness. This is clear also in the case of seven-month children; for because they are incomplete, many of them are born without their passages yet fully articulated, such as those of the ears and nostrils, but these become articulated as the children grow, and many of them go on living. Among human beings, the males become maimed more often than the females, while among the other animals this is no more so. The cause is that among human beings the male differs greatly from the female in the heat of its nature, which is why the males are more prone to movement while in the womb than the females.
45| But because of this motion it is broken more easily; for the young is easily broken because of its weakness. And for this same cause the females reach completion not in the same way as the males in women; for in the mother the female is differentiated from the male over a longer time, but once they have come out, everything is completed earlier in females than in males—for instance puberty, the prime of life, and old age. For females are by nature weaker and colder, and one must suppose that femaleness is, as it were, a natural incapacity. Now inside the womb the female is differentiated slowly because of its coldness (for differentiation is a kind of concoction, and heat concocts, and what is hotter is easily concocted), but outside the womb it reaches its prime and old age quickly because of its weakness; for all lesser things come to their end more quickly, just as in works made by craft, so too in things put together by nature. And because of the cause stated, among human beings twin births of a female and a male survive less often, while among other animals this is no less so; for in humans it is contrary to nature for the two to run an equal course, since the differentiation does not occur in equal times, but the male must necessarily lag behind or the female get ahead, whereas in the other animals this is not contrary to nature.
46| There also occurs a difference regarding pregnancy between human beings and the other animals; for the other animals are in better bodily condition for most of the time, while most women find pregnancy burdensome. Now one cause of this lies also in their way of life; for women who lead sedentary lives are laden with more residue, since among peoples where women's lives involve hard labor, pregnancy is not equally noticeable, and both there and everywhere those accustomed to labor give birth easily; for labor uses up the residues, whereas in sedentary women much of this sort of thing accumulates because of their lack of exertion and because purgations do not occur while they are pregnant, and the labor pain is severe. For labor exercises the breath so that it is able to be held, and it is in this that easy or difficult childbirth consists. Now these factors, as has been said, also contribute to the difference in this affection between the other animals and women, but the chief cause is that in some of the other animals a small purgation occurs, in others none noticeable at all, while in women it is the greatest of all animals; so that when the discharge does not occur because of the pregnancy, it causes disturbance in women; for indeed even when they are not pregnant, when the purgations fail to occur, illnesses result;
47| and at first, most women are disturbed more when they conceive; for the fetus is able to block the purgations, but because of its smallness it does not at first use up any quantity of the residue, while later it relieves them by drawing on it; but in the other animals, because the residue is small, it becomes proportionate to the growth of the embryos, and since the residues that impede nutrition are used up, they are in better bodily condition. And it is the same way among water animals and among birds. But once the fetuses become large, in the cases where the good condition of the body no longer results, the cause is that the growth of the fetus then requires more of the residual nourishment. In a few women it happens that their bodies are in better condition while pregnant; and these are the ones in whom the residues in the body are small, so that they are used up along with the nourishment going to the embryo.
48| We must now speak of the so-called mole, which occurs rarely in women, but occurs as an affection in some who are pregnant. For they give birth to what is called a mole. For it has actually happened to a woman who had intercourse with her husband and believed she had conceived: at first the bulk of her belly grew and everything else proceeded as expected, but when the time for delivery came, she neither gave birth nor did the bulk grow smaller, but continued this way for three or four years, until dysentery set in, and, being in danger from it, she gave birth to a mass of flesh which they call a mole. Moreover this affection grows old along with the woman and dies along with her. Such masses, when they come out into the open, become so hard that they can scarcely be cut through even with iron. Now the cause of this affection has been discussed in the Problems; for the fetus in the womb undergoes the very same thing that things being boiled undergo when they go bad, and this is not because of heat, as some say, but rather because of a weakness of heat. For nature seems to be unable, and incapable of bringing the process to completion or of setting a limit to the generation. This is why it grows old along with the woman or persists for a long time; for it has a nature that is neither that of something completed nor that of something wholly foreign. For the cause of its hardness is failure to concoct; and spoiling too is a kind of failure to concoct. There is a puzzle as to why this does not occur in the other animals, unless it has simply gone unnoticed. We must suppose the cause to be that woman alone among the other animals is subject to disorders of the womb, and has an excess in her purgations and is unable to concoct them; whenever, then, the fetus is formed out of a moisture that is hard to concoct, then what is called the mole occurs in women reasonably either most of all or in them alone.
49| Milk occurs in those females that bear their young alive within themselves, and it is useful for the time of birth. For nature made it, in the form that comes out externally, for the sake of nourishment for animals, so that it neither falls short at all nor is in excess during this period—which is in fact what is seen to happen, unless something occurs contrary to nature. Now in the other animals, because the period of gestation is single, the concoction of it arrives to meet this occasion; but in human beings, since there are several periods, it must be present by the first. This is why before seven months milk is useless to women, but from then on it already becomes useful. And this reasonably comes about also through the cause that operates of necessity, concocted as it is toward the final periods. For at first the secretion of this sort of residue is used up for the generation of the embryos. And of all things, nourishment is the sweetest and most concocted, so that when this power is taken away, what remains must necessarily become salty and bad-tasting. But as the fetuses reach completion, the residue left over becomes greater; for what is used up is less, and it is sweeter, since what is easily concocted is not taken away in the same degree. For the expenditure is no longer directed toward the shaping of the embryo, but toward a small increase, since the embryo is now, so to speak, stationary because it has reached its end.
50| For there is also a kind of completion belonging to the fetus. This is why it comes out and changes the manner of its generation, as having what belongs to it, and no longer taking what does not belong to it, and it is at this time that the milk becomes useful. It collects in the upper region and in the breasts because of the arrangement of the constitution laid down from the beginning. For the region above the diaphragm belongs to the governing part of the animal, and the region below to nourishment and residue, so that whatever animals are capable of locomotion, having in themselves a sufficiency of nourishment, may change places. And it is from here too that the seminal residue is secreted, for the cause stated in the arguments at the beginning. Now both the residue of the males and the menstrual fluid in females are of the nature of blood. And the source of this, and of the veins, is the heart; and this is located among these parts. This is why it is here that the change in this kind of residue must first become noticeable. This is why the voices of both males and females change when they begin to produce seed (for the origin of the voice is from here; and it becomes different as that which moves it becomes different), and the region about the breasts is raised noticeably even in males, but more so in females;
51| For because the excretion occurs downward, the region of the breasts becomes empty in these animals and spongy. And it is the same with those that have their breasts lower down. Now both the voice and the changes about the breasts become noticeable in the other animals too, in those that are experienced about each kind, but in the case of humans it differs most of all. The cause is that in these the residue is greatest in the females among females and in the males among males, in proportion to size — for the females, the residue is the discharge of the menses, for the males, the emission of seed. When, then, the embryo does not take up such a secretion, but prevents it from passing out, the whole residue must necessarily be collected into the empty places — all those that lie on the same passages. And in each case the region of the breasts is of this kind for both causes — it has come to be such both for the sake of the best and from necessity. And it is there that nourishment, once concocted, is already constituted and comes to be for the animals. Of this concoction one can give the cause already stated, and also the opposite one. For it is reasonable that the embryo, being larger, should take up more nourishment, so that less is left over as surplus around this time —
52| and the lesser amount is concocted more quickly. That milk has the same nature as the secretion out of which each thing comes to be is clear, and this has been said before as well. For the matter that nourishes is the same as that out of which nature constitutes the generation. And this, in the blooded animals, is the blood-like fluid. For milk is concocted blood, but not corrupted blood. Empedocles either supposed wrongly or expressed himself badly when he made a poem saying that milk "on the tenth day of the eighth month became white pus." For putrefaction and concoction are opposites, and pus is a kind of putrefaction, while milk belongs among the things concocted. Now the purgations do not occur naturally in nursing women, nor do nursing women conceive; and if they do conceive, the milk is extinguished, because milk and the menses have the same nature. For nature is not able to be so abundant as to serve both purposes at once, but if the secretion goes in one direction, it must necessarily fail in the other, unless this happens under compulsion and contrary to what occurs for the most part. But this is already contrary to nature; for among things that are not incapable of being otherwise but admit of being otherwise, what is in accordance with nature is what occurs for the most part.
53| The generation of animals has also been well determined as to its times. For when, on account of size, the nourishment through the navel is no longer sufficient for the thing carried in the womb, but the milk becomes useful for the nourishment now taking place — and since nourishment no longer enters through the navel — the veins around which the so-called navel-cord is a covering collapse, and it is because of these things that the exit to the outside occurs at that time. The generation of all animals is, in accordance with nature, head-first, because the parts above the navel are larger than those below. For just as things hung from a balance incline toward the weight, so it is here — and the larger parts have more weight.
54| The periods of gestation are, for each of the animals, determined for the most part in accordance with their lifespans. For it is reasonable that the generations of long-lived things should also take longer. This, however, is not really the cause, but it is what happens for the most part; for the larger and more complete of the blooded animals also live for a long time — not, however, that all the larger ones are longer-lived. For of all animals whose experience we have reliable evidence of, man lives the longest time, except for the elephant; yet than that of the bushy-tailed animals and many others. The cause of any animal whatever being long-lived is its being blended in a manner similar to the surrounding air, and certain other natural circumstances, about which we shall speak later; but the cause of the length of the periods of gestation is the size of the things generated. For it is not easy for large compounds — whether of animals or, one might almost say, of anything else — to attain completion in a short time. This is why horses and the animals akin to them, though living a shorter time, are carried a longer time in the womb; for the birth of the one kind comes at a year, while for the other ten months is the longest. For the same cause the gestation of elephants is also long —
55| for the gestation is two years, on account of the excess of size. It is reasonable that the periods of all things — both of gestations, of generations, and of lifespans — should tend to be measured in accordance with nature by cycles. I mean by cycle a day and a night, and a month and a year, and the times measured by these, and further the cycles of the moon. And the cycles of the moon are the full moons and the wanings, and the halvings of the times in between; for it is by these that it stands in relation to the sun, since the month is a cycle common to both. And the moon is a principle on account of its association with the sun and its participation in light; for it comes to be like another, lesser sun; and this is why it contributes to all generations and completions. For heatings and coolings, up to a certain due measure, produce generations, but after this point, destructions. And the movements of these heavenly bodies mark the limit both of the beginning and of the end of these processes. For just as we see the sea, and the whole nature of liquids, standing still and changing in accordance with the movement and rest of the winds, and the air and the winds in accordance with the cycle of the sun and the moon, so too it is necessary that the things growing out of these, and the things within these, should follow suit.