Whether the power's strength causes the generation of a male.
We have already spoken above about the generation of animals," etc.1 One first inquires in this eighteenth book into the differentiation of the sexes. And first one asks whether the strength of the power causes the generation of a male.
1. And it seems not. Power proceeds in a radical way from the heart. For the power is stronger on the side to which the heart inclines more. But the heart's location inclines to the left side; therefore, the power will be stronger there. If, then, the power's strength were the cause of a male, a male would be generated more often on the left side than on the right side. The Philosopher says the opposite.
2. In addition, the male's power prevails over the female's power, because the male's sperm is like a form and an agent [agens] whereas the female's semen is like the matter and that which is acted upon [patiens]. Therefore, if the power's strength were the cause of a male, since the male's power is always stronger, then males would always be generated, since like generates like. This, however, is not true.
The Philosopher says the opposite.
To this some say that the generations of male and female differ with respect to the parts of the womb, since for the most part a male is generated on the right side and a female on the left. But this is not true since the opposite is sometimes found to occur, namely, that a male is on the left side and a female on the right. And sometimes twins are found in one and the same part of the womb, one of which is male and the other female. And besides, if an embryo were generated in the middle of the womb, it would follow, according to this position, that one and the same fetus would be male on the right side and female on the left side, which is unsuitable.
Others say that heat is the principle generating a male and cold is the principle generating a female. But this still cannot be true since, according to this explanation, if an embryo close in disposition to the male were introduced into a cold womb, it would change into the nature of a female, and if a female embryo were introduced into a warm womb, the contrary would occur.
This is why one must respond in accordance with the Philosopher's notion that the strength of the power is the principal cause of a male and its weakness is the cause of a female. For when the power is strong, then the semen is completely digested, and when the power is weak, the menses is rendered almost indigestible. But a male is generated from well digested semen, and this is why the power's strength is the cause of the generation of a male. Thus the positions of all of the others can be reduced to this cause, because very often a male is generated on the right side of the womb, since the heart's influence is greater on the right side and, as a result, its power is stronger there.
Furthermore, strong heat accompanies the strength of the power, and it is the heat's [role] to digest, and this is why some say that heat is the cause of the generation of a male, because heat is an instrument of the power that is a principal cause. This is also why youths (that is, young boys) and old men very often generate females, seeing that youths have not yet achieved strength in their power and old men are deficient in strength.
Moreover, this is also the reason why the north wind causes the generation of a male, and the south wind causes the generation of a female, because the north wind is pure and cleanses and purifies the air and vapors and sharpens the natural powers. But a south wind is humid and rain-filled and is a cause of better digestion. Thus many factors come together as secondary causes [accessoria] for the generation of a male; nevertheless, the strength of the power is the principal cause.
1. On to the arguments. To the first, one must respond that although the heart inclines toward the left side so far as concerns its location, nevertheless it tends toward the right side so far as its influence is concerned.
2. To the second argument one must reply that although the man's sperm is related to the female's semen as an agent relates to matter, nevertheless sometimes the female's semen is disobedient and resists the agent too much, and then the male's power cannot entirely prevail, and this is why it cannot perfectly assimilate the fetus to itself. Instead, it then acts according to the exigency of the matter, and a female is generated.