The Doctrine of Signatures: Understanding the Healing Powers of Plants

The doctrine of Signatures is an age-old theory that explains how humans discovered medicinal uses of plants all across the globe. For thousands of years, people trusted a plant’s appearance could give away its healing properties. 

For example, eye-shaped carrots are good for your eyes. Brain-shaped walnut is actually good for your brain. The heart-shaped Giloy is good for the heart. And there are many more such co-incidences where the shape speaks about its perks. 

Dioscorides wrote, “The Herb Scorpius resembles the tail of the Scorpion, and it is good against biting”. According to Della Porta “Bugloss and Orchanet bear seeds that look like a Viper’s head. And these are good to heal their venomous biting.”

All these symbolic representations are recorded in the doctrine of signatures. Many Researchers wrote how sensory evaluation serves a mnemonic purpose. But many criticised this theory as fanciful and folly.

So, what’s the truth of the Doctrine of Signatures? 

Does nature really work in a way to send out hints to man or is it just man’s imagination?

Well, the views are scattered. Let’s have a look at the very different perceptions:

The doctrine of Signature – The believer’s version

The physical properties of a plant are connected to phytochemical attributes. Like strong odour means the presence of monoterpenes or bitter taste could mean the presence of alkaloids. These factors might be behind the theories of the doctrine of signatures. So, maybe it’s not all blind belief and myths and maybe it’s a kind of a mnemonic device that is of true value.

But very few scholars interpret DOS in a positive light.

Schultes and Hofmann (1980) said, ‘The fear of man may have been a “primitive” result of DOS. But it probably saved many lives. Kreig (1964) quoted, ‘Some of these quaint beliefs had a fragment of truth in it.” 

Plotkin (2000) commented, ’The doctrine has yielded at least one medicinal compound in wide use.” In ancient times, where most of the world only understood symbols, it is likely that the Doctrine of Signatures was useful as a mnemonic aid.

Also Read: Brahmi for Varicose Veins

The Critiques of DOS

If we look at the historical records, there is little evidence that morphological signatures led to the discovery of any medicinal plant. Moreover, the application of the Doctrine of Signatures is largely untestable. There was no research at that time when the utility of medicinal plants was discovered. 

The first critique of this theory was Dodoens (1583). He said, ‘it is so changeable and uncertain that, it seems absolutely unworthy of acceptance”. Hahnemann (1825), the founder of homoeopathy, too ridiculed the theory. His words were, “The ancient physicians determining the medicinal powers of crude drugs from their signatures is a folly.”

Thiselton—Dyer (1889 quoted it as “a backward state of medical science”.

Tyler (1994) ranked this theory among his 10 False Tenets of Paraherbalism. Barford and Kvist (1996) concluded that it is a less promising pharmacological lead than any other medicinal document.

Modern herbals, pharmacopoeias, textbooks, and peer-reviewed literature is condemning DOS. They call it fanciful, far—fetched, premodern, prescientific, primitive, unreliable, and unscientific.

On the Dismissal of Doctrine of Signature 

The late Stephen Jay Gould (2000) provided the most honest assessment of DOS. He said, ‘I question our dismissal as absurd, mystical, or even prescientific. But how can we blame our forebearers for not knowing what later generations would discover? We might as well despise ourselves because our grandchildren will, no doubt, understand the world in a different way.

Modern scholars were not present when traditional healers first learned of the value of medicinal plants. Nor are there any written records of that time. Therefore, it is impossible to say whether signatures influenced plant selection. 

Also, if DOS was the only method of choosing medicinal plants, as many argue, then plants bearing signatures should be more widely used. 

The doctrine of Signatures – Another perspective

There are a number of heart-shaped leaves that should have been mentioned for cardiac disease. A study on heart-shaped leaves yielded 2,584 binomials. The researcher then randomly selected 80 binomials, sampling each. He concluded that of the 80 species, 21 are used medicinally. He found three of the 80 species (less than 4%) are employed in a way that may relate to cardiac medicine. 

Another researcher commented, “In some cases, the signatures of drugs were observed only after the discovery of medicinal use of these plants. So, maybe many valuable herbs were in use before the doctrine. And maybe the organ—plant match was made later.

In a review of anti-inflammatory drugs, Vane and Botting (1998) provided the historical account of the discovery of willow bark. On June 2, 1763, Edward Stone read a report on the use of willow bark in fever. He had accidentally tasted it and was surprised by its extraordinary bitterness. The taste reminded him of cinchona bark (containing quinine), which was used to treat malaria. He believed in the ‘doctrine of signatures, which said cures for diseases would be found in the same locations where the malady occurs. 

Nature of Signatures 

Signatures need not be only morphological.

A common feature of medicinal pharmacopoeias is the strong odour. Plants with potent odour and strong tastes are employed in medicine. These sensory cues are correlated with the presence of bioactive compounds. It is no coincidence that herbs and spices possess antimicrobial activity.

DOS’s Role As A Mnemonic 

An association of medicine with a signature makes it easier to remember. It also becomes easy to transmit knowledge about its use. Its utility as a memory aid was first suggested in 1938 by Buchanan (1991 [orig. 1938]) and later mentioned by Etkin (1988), James (n.d.), and Leonti et al. (2002). 

Mnemonic cues may be essential to the viability of knowledge transmission. Plants that are both efficacious and easy to remember are more likely to be used in the non—literate societies through time.

The role of mnemonic in cultural transmission is well established. 

Physicians, burdened with vast indications, counter-indications, and cures can use a simple mnemonic to remember the anticholinergic poisonings: red as a beet, hot as a hare, blind as a bat, dry as a bone, and mad as a hatter. 

Conclusions 

The Doctrine of Signatures is found throughout the world. And it has been in use for centuries. So, before dissing it as some primitive and prescientific date, we should look at the broader and logical perspectives too. 

It’s true that everything that resembles a signature may not be medicinally helpful. But if there is a symbolization of the plants then it becomes easier to retain and transfer the knowledge. So, DOS does have some value to offer to this modern world too!