Teratology. In the early 1800s, a new science of monstrosities was promoted by the French anatomist Etienne Geoffroy Saint-Hilaire (1772–1844). His claim that all animals could be reduced to a single basic plan, linking the lowest organisms with man, challenged the strict religious and political hierarchy. Geoffroy argued that monsters are products of environmental changes during development and set out to prove his theory by mechanically damaging incubated chick eggs. Although these experiments failed, his attempts to explain and categorize monsters were followed up by the next generation of anatomists, most prominently his son and successor, Isidore (1805–61). Isidore’s three-volume book ambitiously ordered all congenital deviations from the norm, from benign anatomical varieties to fatal monstrosities, into an overarching and successful nomenclature.


From portents of divine messages and wonders of nature, monsters were transformed into proofs of developmental laws.

Before the eighteenth century, ‘monsters’—malformed, often aborted or still-born animals and (occasionally) children—were seen as wondrous singularities of nature. In the contemporary culture of spectacle, they were displayed in ‘cabinets of curiosities’. Monsters also carried divine messages. In the 1400s they signified God’s anger at such vices as sodomy or pride; in the politically and religiously charged atmosphere of the Reformation and the English Civil War they portended heresy. Only with the end of the religious wars in the late 1600s did naturalistic causes gain prominence. These included excess of seed and the maternal imagination: the belief that a woman’s thoughts affect the form of the child.

By the late 1600s, monsters became a key bone of contention in debates over generation. They particularly troubled advocates of pre-existence, for why would God have created such germs? Grouping monsters together eventually made clear that, far from singular, they conformed to certain regular laws. Supporters of epigenesis argued that monsters were outcomes of an excessive or deficient developmental force. Studying the timing and nature of obstructive events pointed towards crucial moments in the formation of an embryo. No longer wonders, monsters could now teach about normal development.

The political monster, 1523


Monsters as proofs of developmental laws, 1791