In wild plants, the secondary compounds, not directly involved in plant physiology, are considered as resulting from the selective pressure exerted by microbes and phytophagous invertebrates and vertebrates, providing protection from predators and pathogens. Secondary plant metabolites occur usually only in special, differentiated cells and their chemical structure is invariably more complex than that of primary metabolites. Many of these secondary metabolites are toxic and more than 50000 different substances have been identified so far (e.g. Alkaloids, Glycosides, Terpenes, etc.).Ironically such non-nutritional metabolites, generally toxic or inhibiting consumption by reducing palatability or digestibility, are the major source of drugs for humans in nowadays medicine. The classic example is Morphine, one Alkaloid produced by Papaver somniferum. The limit between poison and medicine is often based on the dose. Morphine can be an excellent analgesic, but in higher doses may lead to apnea and consecutive death.
A growing body of evidence shows that animals such as insects, birds and primates use plant parts with secondary compounds to improve their comfort or their health. The concept of self-medication, now generally accepted in primates but also in other vertebrates was first proposed by Daniel H Janzen (1978), an ecologist at the University of Pennsylvania. Taste perception may be a major clue for such a specific choice. Bitterness is suggested to represent a reliable signal of toxicity for animals and humans. A number of secondary compounds are bitter tasting (Saponins, Alkaloids and some Sesquiterpenoids, Terpenoids and Steroid Glycosides) and many of these substances possess important pharmacological activity.
Primates even seem to use plants as stimulants / psychoactive drugs! One very interesting case are Chacma baboons (Papio ursinus) in South Africa, who consume a little quantity of leaves of specific plants, which are well known for their psychoactive properties each day. The consumption of such plants is not directly related to any illness or a diseased state. These include Datura innoxia and Datura stramonium (Solanaceae), which are also used by traditional societies for their hallucinogenic potential.
What’s known about the use of herbal medicine at Paleolithic times? The most cited, but unfortunately ambiguous case is that Shanidar excavated by Ralph Solecki of Columbia University over a series of four field seasons between 1951 and 1960.
Shanidar Cave is located in the Zagros Mountains of northern Iraq. It is one of a number of caves and rock shelters in the drainage of the Greater Zab River, a major tributary of the Tigris. The archaeological sequence in the cave included Middle Paleolithic, Upper Paleolithic, and PPN occupations. Level D, the lowest stratigraphic unit, produced Non-Levallois Mousterian tools and eight skeletons described as Neanderthals. Four of the individuals are thought to have been killed by rock falls in the cave, while the others, including Shanidar skeleton IV, appear to have been deliberately buried. Soil samples were collected from within and outside of the area of the Shanidar IV skeleton. Later analysis of these samples revealed that, in general, throughout the cave, pollen was poorly represented. Two samples from around the Shanidar IV burial, however, were substantially different. These samples, evaluated by A Leroi-Gourhan contained a much higher number of pollen grains, many of which were in clusters indicating that complete flowers were deposited. Of the 28 species of pollen that were identified, seven occurred in clusters, and these species accounted for the majority of the pollen recovered. The identified pollen consists of, in order of decreasing frequency, Compositae, Chenopods, Gramineae, Caryophylaceae, Ephedra, Dispacaceae, Artemisia, and several others. The seven pollen types that were recovered in clusters interpreted as representing whole flowers include Achillea sp. (yarrow), Senecio sp. (groundsel), Centaurea solstitialis (St Barnaby’s thistle), Muscari sp. (grape hyacinth), Ephedra altissima (woody horse tail), and two unidentified species.
Solecki has pointed out that most of the flowers are known to have herbal properties, and are used by the people of the region today. Leroi-Gourhan interpreted the pollen evidence as indicating that during spring more than 50,000 years ago, the body of Shanidar IV was laid on a bed of woody branches (Ephedra) and flowers (the Compositae types, the unidentified types, and Muscari). Presumably the Chenopods, Gramineae, Caryophylaceae, Dispacaceae, and Artemisia represent background pollen that was naturally incorporated into the burial fill.
However, not everyone has agreed with the hypothesis that the placement of the flowering plant offerings at the burial site was a conscious choice of the Neanderthals. The original report described the existence of animal holes around the burial along with the fossil remains of the “Persian jird” (Meriones persicus). This rodent species lives in large colonies and is known to store large amount of seeds and flowers in its burrows. Indeed excavators identified numerous jird, burrows near the burial, and 70% of all the rodent bone recovered from Shanidar Cave was from this jird species. Analysis of jird burrows has also revealed the remains of many of the same flowers that were found around Shanidar IV. Thus the presence of flower pollen around the skeleton may not have been the result of ritualistic activity, but simply the establishment of jird burrows following the burial (Sommer 1998).
The story goes on, however. Researchers from different countries combined pyrolysis gas-chromatography-mass spectrometry with morphological analysis of plant microfossils to identify material trapped in dental calculus from five Neanderthals from the north Spanish site of El Sidrón. Discovered in 1994, El Sidrón contained around 2,000 skeletal remains of at least 13 individuals dating back 50 k.a. BP. It seems that the new data substantiate earlier assumptions about the use of medicinal plants by Neanderthals. The research team found starch granules and carbohydrate markers in the samples, plus evidence for secondary plant compounds such as azulenes and coumarins, as well as possible evidence for nuts, grasses and even green vegetables.
Lead author K Hardy, from the Universitat Autònoma de Barcelona argues that: “The varied use of plants we identified suggests that the Neanderthal occupants of El Sidrón had a sophisticated knowledge of their natural surroundings which included the ability to select and use certain plants for their nutritional value and for self-medication. While meat was clearly important, our research points to an even more complex diet than has previously been supposed.”
Earlier research had shown that the Neanderthals in El Sidrón had the bitter taste perception gene. Now the excavation team had found molecular evidence that one individual had even eaten bitter tasting plants most probably for self-medication. This is molecular archaeolgy at its best!
Especially the presence of chamazulene in the sample is notable since the compound occurs in yarrow (Achillea millefolium) and in camomile (Matricaria chamomilla). These herbs, widely used in self-medication in preindustrial Europe have moderate antioxidant and antimicrobial activities, and a significant antiplatelet activity in vitro. Animal model studies indicate potent anti-inflammatory as well as antispasmodic and anxiolytic effects.