“It is therefore apparent that there are three ranks of events: the miraculous, the natural, and the voluntary. And the miraculous is not at all governed by the others or their laws, but freely governs; nor does it harm them, when it seems to come up against them, because they have nothing but what they have received from it, nor has it given to them anything except what is under it.
Thus if the propagation of a man from a virgin is not voluntary or natural but miraculous, like that which brought forth a woman from a man alone, and like the creation of man from clay, it is clear that it cannot submit to the laws and merits of that propagation which nature and the will although separately—work. For here the will does one thing and nature another. But equally Adam is a man taken from a non-human, and Jesus from a woman alone and Eve from a man alone, as much as any man or woman from a man and a woman.
But every man is either Adam or born of Adam; but Eve is from Adam alone, and all others from Adam and Eve. Mary, from whom alone Jesus comes, is of Adam and Eve; therefore he cannot but be born of them. Thus it was expedient that he who was to redeem the human race should have his being and birth from the father and mother of us all.”
-Anselm of Canterbury, On the Virgin Conception and Original Sin, 11.