More and more, as the organic world was observed, the vast multitude of petty animals, winged creatures, and "creeping things" was felt to be a strain upon the sacred narrative.

More and more it became difficult to reconcile the dignity of the Almighty with his work in bringing each of these creatures before Adam to be named; or to reconcile the human limitations of Adam with his work in naming "every living creature"; or to reconcile the dimensions of Noah's ark with the space required for preserving all of them, and the food of all sorts necessary for their sustenance, whether they were admitted by twos, as stated in one scriptural account, or by sevens, as stated in the other.
The inadequate size of the ark gave especial trouble.

Origen had dealt with it by suggesting that the cubit was six times greater than had been supposed.

Bede explained Noah's ability to complete so large a vessel by supposing that he worked upon it during a hundred years; and, as to the provision of food taken into it, he declared that there was no need of a supply for more than one day, since God could throw the animals into a deep sleep or otherwise miraculously make one day's supply sufficient; he also lessened the strain on faith still more by diminishing the number of animals taken into the ark--supporting his view upon Augustine's theory of the later development of insects out of carrion.
Doubtless this theological necessity was among the main reasons which led St.Isidore of Seville, in the seventh century, to incorporate this theory, supported by St.Basil and St.Augustine, into his great encyclopedic work which gave materials for thought on God and Nature to so many generations.

He familiarized the theological world still further with the doctrine of secondary creation, giving such examples of it as that "bees are generated from decomposed veal, beetles from horseflesh, grasshoppers from mules, scorpions from crabs," and, in order to give still stronger force to the idea of such transformations, he dwells on the biblical account of Nebuchadnezzar, which appears to have taken strong hold upon medieval thought in science, and he declares that other human beings had been changed into animals, especially into swine, wolves, and owls.
This doctrine of after-creations went on gathering strength until, in the twelfth century, Peter Lombard, in his theological summary, The Sentences, so powerful in moulding the thought of the Church, emphasized the distinction between animals which spring from carrion and those which are created from earth and water; the former he holds to have been created "potentially" the latter "actually." In the century following, this idea was taken up by St.Thomas Aquinas and virtually received from him its final form.