Athens, 4th cent. B.C. (Aristotle, On the Generation of Animals, 716a5-23, 727a2-30, 727b31-33, 728b l8-31, 765b8-20, 766al7-30, 783b26-784al2. Tr. A.L. Peck, LCL. G)

Aristotle’s explanation of the process of conception is deduced from external secretions: male semen has primary generative importance, female semen (i.e. menstrual fluid, which also sustains the developing embryo) purely nutritive value.

Male and female defined

As far as animals are concerned, we must describe their generation just as we find the theme requires for each several kind as we go along, linking our account on to what has already been said. As we mentioned, we may safely set down as the chief principles of generation the male [factor] and the female [factor]; the male as possessing the principle of movement and of generation, the female as possessing that of matter. One is most likely to be convinced of this by considering how the semen is formed and whence it comes; for although the things that are formed in the course of Nature no doubt take their rise out of semen, we must not fail to notice how the semen itself is formed from the male and the female, since it is because this part is secreted from the male and the female, and because its secretion takes place in them and out of them, that the male and the female are the principles of generation. By a ‘male’ animal we mean one which generates in another, by ‘female’ one which generates in itself. This is why in cosmology too they speak of the nature of the earth as something female and call it ‘mother’, while they give to the heaven and the sun and anything else of that kind the title of ‘generator’, and ‘father’. Now male and female differ in respect of their logos in that the power or faculty possessed by the one differs from that possessed by the other; but they differ also to bodily sense, in respect of certain physical parts. They differ in their logos, because the male is that which has the power to generate in another (as was stated above), while the female is that which can generate in itself, i.e. it is that out of which the generated offspring, which is present in the generator, comes into being …[1]

Male and female secretions

This much is evident: the menstrual fluid is a residue, and it is the analogous thing in females to the semen in males. Its behaviour shows that this statement is correct. At the same time of life that semen begins to appear in males and is emitted, the menstrual discharge begins to flow in females, their voice changes and their breasts begin to become conspicuous; and similarly, in the decline of life the power to generate ceases in males and the menstrual discharge ceases in females. Here are still further indications that this secretion which females produce is a residue. Speaking generally, unless the menstrual discharge is suspended, women are not troubled by haemorrhoids or bleeding from the nose or any other such discharge, and if it happens that they are, then the evacuations fall off in quantity, which suggests that the substance secreted is being drawn off to the other discharges. Again, their blood vessels are not so prominent as those of males; and females are more neatly made and smoother than males, because the residue which goes to produce those characteristics in males is in females discharged together with the menstrual fluid. We are bound to hold, in addition, that for the same cause the bulk of the body in female vivipara[2] is smaller than that of the males, as of course it is only in vivipara that the menstrual discharge flows externally, and most conspicuously of all in women, who discharge a greater amount than any other female animals. On this account it is always very noticeable that the female is pale, and the blood-vessels are not prominent, and there is an obvious deficiency in physique as compared with males.

Now it is impossible that any creature should produce two seminal secretions at once, and as the secretion in females which answers to semen in males is the menstrual fluid, it obviously follows that the female does not contribute any semen to generation; for if there were semen, there would be no menstrual fluid; but as menstrual fluid is in fact formed, therefore there is no semen …

There are some who think that the female contributes semen during coition because women sometimes derive pleasure from it comparable to that of the male and also produce a fluid secretion. This fluid, however, is not seminal; it is peculiar to the part from which it comes in each several individual; there is a discharge from the uterus, which though it happens in some women does not in others. Speaking generally, this happens in fair-skinned women who are typically feminine, and not in dark women of a masculine appearance. Where it occurs, this discharge is sometimes on quite a different scale from the semen discharged by the male, and greatly exceeds it in bulk. Furthermore, differences of food cause a great difference in the amount of this discharge which is produced: e.g. some pungent foods cause a noticeable increase in the amount … 

Further, a boy actually resembles a woman in physique, and a woman is as it were an infertile male; the female, in fact, is female on account of inability of a sort, viz. it lacks the power to concoct semen out of the final state of the nourishment (this is either blood, or its counterpart in bloodless animals) because of the coldness of its nature. Thus, just as lack of concoction produces in the bowels diarrhoea, so in the blood vessels it produces discharge of blood of various sorts, and especially the menstrual discharge (which has to be classed as a discharge of blood, though it is a natural discharge, and the rest are morbid ones).

Hence, plainly, it is reasonable to hold that generation takes place from this process; for, as we see, the menstrual fluid is semen, not indeed semen in a pure concoction, but needing still to be acted upon. It is the same with fruit when it is forming. The nourishment is present right enough, even before it has been strained off, but it stands in need of being acted upon in order to purify it. That is why when the former is mixed with the semen, and when the latter is mixed with pure nourishment the one effects generation, and the other effects nutrition …

The role of heat

Now the opinion that the cause of male and female is heat and cold, and that the difference depends upon whether the secretion comes from the right side or from the left, has a modicum of reason in it, because the right side of the body is hotter than the left; hotter semen is semen which has been concocted; the fact that it has been concocted means that it has been set and compacted, and the more compacted semen is, the more fertile it is. All the same, to state the matter in this way is attempting to lay hold of the cause from too great a distance, and we ought to come as closely to grips as we possibly can with the primary causes.

We have dealt already elsewhere with the body as a whole and with its several parts, and have stated what each one is, and on account of what cause it is so. But that is not all, for (l) the male and the female are distinguished by a certain ability and inability. Male is that which is able to concoct, to cause to take shape, and to discharge, semen possessing the ‘principle’ of the ‘form’; and by ‘principle’ I do not mean that sort of principle out of which, as out of matter, offspring is formed belonging to the same kind as its parent, but I mean the proximate motive principle, whether it is able to act thus in itself or in something else. Female is that which receives the semen, but is unable to cause semen to take shape or to discharge it. And (2) all concoction works by means of heat. Assuming the truth of these two statements, it follows of necessity that (3) male animals are hotter than female ones, since it is on account of coldness and inability that the female is more abundant in blood in certain regions of the body. And this abundance of blood is a piece of evidence which goes to prove the opposite of the view held by some people, who suppose that the female must be hotter than the male, on account of the discharge of menstrual fluid.

When the ‘principle’ is failing to gain the mastery and is unable to effect concoction owing to deficiency of heat, and does not succeed in reducing the material into its own proper form, but instead is worsted in the attempt, then of necessity the material must change over into its opposite condition. Now the opposite of the male is the female, and it is opposite in respect of that whereby one is male and the other female. And since it differs in the ability it possesses, so also it differs in the instrument which it possesses. Hence this is the condition into which the material changes over. And when one vital part changes, the whole make-up of the animal differs greatly in appearance and form. This may be observed in the case of eunuchs; the mutilation of just one part of them results in such a great alteration of their old semblance, and in close approximation to the appearance of the female. The reason for this is that some of the body’s parts are ‘principles’, and once a principle has been ‘moved’ (i.e. changed), many of the parts which cohere with it must of necessity change as well …

Also, the fact that the menstrual discharge in the natural course tends to take place when the moon is waning is due to the same cause. That time of month is colder and more fluid on account of the waning and failure of the moon (since the moon makes a summer and winter in the course of a month just as the sun does in the course of the whole year) …

So that if you reckon up (a) that the brain itself has very little heat, (b) that the skin surrounding it must of necessity have even less, and (c) that the hair, being the furthest off of the three, must have even less still, you will expect persons who are plentiful in semen to go bald at about this time of life.[3] And it is owing to the same cause that it is on the front part of the head only that human beings go bald, and that they are the only animals which do so at all; i.e. they go bald in front because the brain is there, and they alone do so, because they have by far the largest brain of all and the most fluid. Women do not go bald because their nature is similar to that of children: both are incapable of producing seminal secretion. Eunuchs, too, do not go bald, because of their transition into the female state, and the hair that comes at a later stage they fail to grow at all, or if they already have it, they lose it, except for the pubic hair: similarly women do not have the later hair, though they do grow the pubic hair. This deformity constitutes a change from the male state to the female.


1. Cf. Apollo’s argument in Aeschylus, Eumenides 658-61, which helps win the case for Orestes: ‘She who is called the child’s mother is not its begetter, but the nurse of the newly sown conception. The begetter is the male, and she as a stranger for a stranger preserves the offspring, if no god blights its birth’ (tr. H. Lloyd-Jones).

2. Animals that give birth to live offspring, as opposed to those that lay eggs.

3. In the Hippocratic Corpus (On the Nature of the Child 20), baldness is also attributed to excess fluid.