Plants have been the cornerstone of medicinal therapies for thousands of years and continue to be an essential part of health care for much of the world. The traditional origins of many current pharmaceuticals have been obscured by the process of drug development, such as aspirin from willow bark (Salix spp.), reserpine for hypertension from the Indian Snake Root (Rauwolfia serpentina) and D-tubocurarine, widely used as a muscle relaxant in surgery, from arrow poisons (Chondodendron tomentosum, as discussed earlier), but the plants used in traditional medicine continue to supply the industry with raw materials and new ideas. Of the frequently quoted 25% of prescription drugs sold in North America that contain active principles derived from plants (Farnsworth, 1988), three-quarters were initially recognized by the industry because of their use in traditional medicine (Farnsworth, 1990). The current directions in the industry, however, are not so much determined by swashbuckling histories, as by which screening methodologies generate the best new drug leads.
Ethnobotany is just one strategy for discovering new compounds, but the pharmaceutical businesses that have chosen to focus on leads from traditional medicines have not based their decisions on altruism alone. To test this approach a theory of species sampling described as the ethno-directed sampling hypothesis was proposed. It maintains that using the combination of indigenous knowledge and ethnobotanical documentation as a pre-screen will allow the researcher to obtain a higher number of leads in a pool of plant samples compared with a group of plants selected at random (Balick, 1990). In an initial test of the hypothesis, plant samples from Belize and Honduras were subjected to an human immunodeficiency virus (HIV) screening by the National Cancer Institute (NCI). Six per cent of the random collections indicated activity, whereas 25% of the ethnobotanical collections were active (Balick, 1990). More recent studies using in-vitro and in-vivo screens with traditional pharmacopoeia continue to show high rates of pharmacological activity. In a screening of plant species used as medicine by indigenous communities in Samoa, over 86% displayed significant chemical activity (Cox, 1990). Screening results from a newly established company, Shaman Pharmaceuticals, have revealed that of the samples that displayed promising chemical activity, 74% directly correlated with the original ethnobotanical use (King, 1992).
The NCI recently re-embarked on medicinal plant research in the mid-1980s, initiating species collection in many different parts of the world. In a sample of NCI's latest screenings for activity against HIV, less than 2% of the random species collections showed in-vitro activity worth pursuing further in the laboratory, whereas over 15% of the ethnobotanical collections indicated preliminary chemical activity against the virus (M.J. Balick, unpublished data), later attributed to other compounds with previously known anti-viral effects such as tannins and polysaccharide. These were not pursued as this search was limited to 'novel' compounds.
The depth and breadth of ethnobotanical research to date has been conducted almost as spottily as the research on biological diversity. Explorers and field researchers have not systematically and consistently targeted the most likely leads first. The focus of research has been shaped by many external factors including geographic access, funding stipulations, language barriers and chance. Hence, it seems unlikely that the potential of future discovery has been significantly diminished by the subtraction of each new compound from the pool of information. With the increasing importance of supply issues, in concert with the pursuit of new products, it is probable that ethnobotany will continue to provide as valuable leads in the future as it has in previous decades and centuries.
Natural products and individual cultures pose significant obstacles for industries which are striving to maintain consistent levels of quality and supply on a large scale. The costs involved in finding and isolating useful compounds, developing a product and out maneuvering the competition often seem to outweigh the potential benefits of any therapy short of the cure for cancer. Many of the major pharmaceutical companies were founded on the commercialization of products derived from plants, but most have largely converted to synthetic production and cut back on natural product research (Farnsworth, 1988). More recently the limitations of the ability of modern medicine to cure and the growing specialty markets for herbals and alternative medicines (Angier, 1993) have reversed this trend and many companies are again investing in the search for interesting natural products (Shaffer, 1992).
Pharmaceutical companies have developed mass screening programs to accommodate a large volume of botanical samples. These screening processes are capital intensive and usually rely on spotting chemical actions that have been previously recognized in the laboratory and are already understood. A recent departure from this approach is an effort currently underway at Shaman Pharmaceuticals, located in San Francisco, California. Shaman's strategy is to develop more efficient discovery processes by focusing on plants with a history of human medicinal use (Shaman, 1993), species whose activity has been recognized in a traditional context. They hope thereby to significantly increase their rate of success and cut the investment of time and capital required to prove a drug successful and to take it to market. In their initial charter, Shaman established a parallel non-profit-making company called The Healing Forest Conservancy to address the needs and rights of the communities in which they conduct ethnobotanical research. This effort to recognize the value of wild species, ecosystems and traditional knowledge is aimed at bridging the seemingly divergent interests of both traditional people and Western consumers (Shaman, 1993). Although driven by shareholders' interests, the company has consciously linked their success as a business to their ability to protect the resources on which their business is founded.
Even though industry's interest in the potential of biological diversity and traditional knowledge may stimulate a new wave of investment in ethnobotanical research, there are many historic examples of demand overrunning formerly abundant natural resources, as well as the cultural practices that once protected them (King, 1992). Developing markets for natural products, particularly those that are harvested from the wild, can trigger a demand that cannot be met by available or legal supplies (Ehrenfeld, 1992). Although sustainability is widely used to describe management practices which do not damage the distribution and genetic integrity of a plant population over the long term, what these practices actually are must be determined on a species basis (Foster, 1991). Since most industries have more experience with marketing than with determining levels of sustainability, levels of sustainability are often developed more according to levels of demand than to actual population dynamics of a natural supply. It is probable that many more so-called green products are sold than could potentially be 'sustainably' harvested (Shaffer, 1993). Developing a better understanding of resource availability and renewability is an essential aspect to the development of truly green products (Toledo et ah, 1992).
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