Doctrine of signatures

The doctrine of signatures is a non-scientific theory based on the exterior characteristics of plants showing a resemblance to parts of the human body. These resemblances would supposedly contained clues about the parts of the human body they could be used for. According to this doctrine, a walnut, for instance, would be good for your brain, since a walnut looks like a brain. While it’s true that the fatty acids in a walnut are important for the functioning of that organ, that comparison is based on coincidence. Those same fatty acids can be found in nuts that look nothing like a brain.

The Christian tradition of the late Middle Ages added an extra layer to the doctrine of signatures. The shape of the plant or fruit, combined with the healing powers, was seen as proof of God. The will to explain the unexplainable thus nestled itself deep within the early modern scientific tradition.

Mandrake was seen as such a proof of God as well. Pythagoras had already observed how the roots looked like mini-people. Up until the 17th century, we can find examples of naturalist scholars publishing protobiologies about the fantasy-tickling roots of the plant.

A great example of such a publication is kept in the library of Rijksmuseum Boerhaave. This 17th century ‘monster book’by the Italian Uylsse Aldrovandi (1557-1602) describes, besides fantastic beasts such as seahorses, dragons and phoenixes, all kinds of human and plant-like growths or ‘monstrosities’. They described in the full title of the book as well: Vlyssis Aldrovandi patricii Bononiensis Monstrorvm historia : cvm Paralipomenis historiæ omnivm animalivm_.

Aldrovandi was an Italian naturalist scholar from Bologona famous for being the driving force behind the founding of the botanical garden of the University of Bologona, the oldest university in the world. His natural-historical collection can still be found in the part of the Palazzo Poggi museum of the university city that was dedicated to him.

In the chapter on botany, Aldrovandi describes the mandrake root and its special shape. The image is a true-to-life image of a root that seems to have a slightly human shape. The interesting thing about this, is that in this engraving, compared to an earlier botanic image, he leaves nothing to the imagination. His Erbario Alchemico contains an image that clearly shows a human face drawn on the mandrake root. Here we see the disenchantment of the world as a result of the scientific revolution as it took place around 1600. Fantasy gave way to ratio.