Did St. Aquinas really have a recipe for making mice?
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Like many of his contemporaries, Thomas Aquinas (1224–1274) believed in the spontaneous generation of insects and vermin. The doctrine of spontaneous generation held that life could literally just appear without the prior presence of parent organisms. This biological mythology went back to Aristotle and is in fact strangely empirical, if you think about it. Flies, for example, do suddenly seem to appear out of rotting garbage. It took a long time—well into the seventeenth century—to discover that the maggots they spring from come from eggs laid by parent flies.
Aquinas thought that insects sprang to life in filth, owing to the Devil’s influence. He thought that the development of mice, however, depended on changes in the positions of the stars. As “proof” of this origin of baby mice, Aquinas had a recipe: Take some old rags and wheat and leave them undisturbed in a drawer for a while (to give the stars enough time to exert their effects) and then take a peek. Again, there is a crude empiricism at work here. If there are mice in a dwelling, its inhabitants rarely see them breed, and rarer still do they observe female mice building nests and giving birth. If this has happened in a neglected drawer, all that may be evident when one suddenly opens it is the litter of pink babies when the last time one looked there was nothing but old rags and wheat. (If you try this at home, the wheat is probably unnecessary, although the mother mouse will doubtless appreciate it.)