Objection 1. It would seem that in the primitive state woman would not have been born. For the Philosopher says (De Gener. Animal. ii, 3) that woman is a "misbegotten male," as though she were a product outside the purpose of nature. But in that state nothing would have been unnatural in human generation. Therefore in that state women would not have been born.
Objection 2. Further, every agent produces its like, unless prevented by insufficient power or ineptness of matter: thus a small fire cannot burn green wood. But in generation the active force is in the male. Since, therefore, in the state of innocence man's active force was not subject to defect, nor was there inept matter on the part of the woman, it seems that males would always have been born.
Objection 3. Further, in the state of innocence generation is ordered to the multiplication of the human race. But the race would have been sufficiently multiplied by the first man and woman, from the fact that they would have lived for ever. Therefore, in the state of innocence, there was no need for women to be born.
On the contrary, Nature's process in generation would have been in harmony with the manner in which it was established by God. But established male and female in human nature, as it is written (Genesis 1-2). Therefore also in the state of innocence male and female would have been born.
I answer that, Nothing belonging to the completeness of human nature would have been lacking in the state of innocence. And as different grades belong to the perfection of the universe, so also diversity of sex belongs to the perfection of human nature. Therefore in the state of innocence, both sexes would have been begotten.
Reply to Objection 1. Woman is said to be a "misbegotten male," as being a product outside the purpose of nature considered in the individual case: but not against the purpose of universal nature, as above explained (92, 1, ad 2).
Reply to Objection 2. The generation of woman is not occasioned either by a defect of the active force or by inept matter, as the objection proposes; but sometimes by an extrinsic accidental cause; thus the Philosopher says (De Animal. Histor. vi, 19): "The northern wind favors the generation of males, and the southern wind that of females": sometimes also by some impression in the soul (of the parents), which may easily have some effect on the body (of the child). Especially was this the case in the state of innocence, when the body was more subject to the soul; so that by the mere will of the parent the sex of the offspring might be diversified.
Reply to Objection 3. The offspring would have been begotten to an animal life, as to the use of food and generation. Hence it was fitting that all should generate, and not only the first parents. From this it seems to follow that males and females would have been in equal number.
Source: Summa Theologica (New Advent)