Objection 1. It would seem that in the state of innocence all would have been equal. For Gregory says (Moral. xxi): "Where there is no sin, there is no inequality." But in the state of innocence there was no sin. Therefore all were equal.
Objection 2. Further, likeness and equality are the basis of mutual love, according to Sirach 13:19, "Every beast loveth its like; so also every man him that is nearest to himself." Now in that state there was among men an abundance of love, which is the bond of peace. Therefore all were equal in the state of innocence.
Objection 3. Further, the cause ceasing, the effect also ceases. But the cause of present inequality among men seems to arise, on the part of God, from the fact that He rewards some and punishes others; and on the part of nature, from the fact that some, through a defect of nature, are born weak and deficient, others strong and perfect, which would not have been the case in the primitive state. Therefore, etc.
On the contrary, It is written (Romans 13:1): "The things which are of God, are well ordered" [Vulg."Those that are, are ordained of God"]. But order chiefly consists in inequality; for Augustine says (De Civ. Dei xix, 13): "Order disposes things equal and unequal in their proper place." Therefore in the primitive state, which was most proper and orderly, inequality would have existed.
I answer that, We must needs admit that in the primitive state there would have been some inequality, at least as regards sex, because generation depends upon diversity of sex: and likewise as regards age; for some would have been born of others; nor would sexual union have been sterile.
Moreover, as regards the soul, there would have been inequality as to righteousness and knowledge. For man worked not of necessity, but of his own free-will, by virtue of which man can apply himself, more or less, to action, desire, or knowledge; hence some would have made a greater advance in virtue and knowledge than others.
There might also have been bodily disparity. For the human body was not entirely exempt from the laws of nature, so as not to receive from exterior sources more or less advantage and help: since indeed it was dependent on food wherewith to sustain life.
So we may say that, according to the climate, or the movement of the stars, some would have been born more robust in body than others, and also greater, and more beautiful, and all ways better disposed; so that, however, in those who were thus surpassed, there would have been no defect or fault either in soul or body.
Reply to Objection 1. By those words Gregory means to exclude such inequality as exists between virtue and vice; the result of which is that some are placed in subjection to others as a penalty.
Reply to Objection 2. Equality is the cause of equality in mutual love. Yet between those who are unequal there can be a greater love than between equals; although there be not an equal response: for a father naturally loves his son more than a brother loves his brother; although the son does not love his father as much as he is loved by him.
Reply to Objection 3. The cause of inequality could be on the part of God; not indeed that He would punish some and reward others, but that He would exalt some above others; so that the beauty of order would the more shine forth among men. Inequality might also arise on the part of nature as above described, without any defect of nature.
Source: Summa Theologica (New Advent)