Doctrine of signatures

The doctrine of signatures, also known as the doctrine of correspondences, states that herbs or animals have physical or behavioral traits that mirror the ailment it can successfully treat.^[1] Theological justifications, such as that of botanist William Cole, were that God would want to show men what plants would be useful for.^[2] The doctrine of signatures has a debated origin.^[3] Many historians believe it begins with primitive thinking methods, while other historians believe it originated with Dioscorides and was popularized in the 16th and 17th centuries after Jakob Böhme coined the doctrine of signatures in his book The Signature of All Things.^[2][3][4]

This theory is a possible explanation for the ancient discovery of medicinal properties; however, there is no definitive proof as to whether the medicinal property or the connection in physical/behavioral traits was realized first.^[5] The theory later became a scientific basis for trying new remedies solely based upon their qualities in an attempt to find new medicines. While there are some homeopathic remedies that are still used today which have been connected to this theory, there are also remedies from this theory which have been found harmful.^[1][6] For instance, birthwort (so-called because of its resemblance to the uterus) was once used widely for pregnancies, but is carcinogenic and very damaging to the kidneys, owing to its aristolochic acid content.^[7] As a defense against predation, many plants contain toxic chemicals, the action of which is not immediately apparent or easily tied to the plant rather than other factors.