This article appeared in the
in The Textbook Letter, July-August 1999.
The rain-forest claptrap in Holt, Rinehart and Winston's high-school book Holt Health is especially bad because the Holt writers try to kill two toucans with one stone. In an article headlined "Cultural Diversity: Medicines From the Rain Forest" they promote the common fancy that tropical rain forests are huge storehouses of pharmaceutical materials, and they also pander to the multi-culti mob by depicting rain-forest indigenes as medical savants.
Holt's writers announce that indigenous rain-forest "cultures" have "contributed a tremendous amount to the contents of our medicine cabinets" -- but the writers are unable to name even one substance that may exemplify that "tremendous" contribution [see note 1, below]. Instead, they quickly change the subject and recite some fluff about quinine and curare (which very few of us keep in our medicine cabinets or anywhere else). Then they say:
Finally, nearly 70 percent of the plants known to be useful in the treatment of cancer come from the rain forests. We know about most of these cancer-fighting plants from the native people who live where the plants grow.
Here again Holt's writers fail to support their story. They don't name any "plants known to be useful in the treatment of cancer," and they don't even tell what that phrase means. (Who treats cancer with plants? Where? How?) They don't support their "native people" claim, either -- because they can't. They are dispensing disinformation, and they have contrived their vague, ambiguous "native people" statement to foster a notion that's bogus: They want students to think that most of what we know about the use of botanical materials as antineoplastic agents (i.e., agents that suppress cancers) is attributable to tribal folklore, rather than to scientific research.
Indeed, the writers' entire attempt to link tropical rain forests with "cancer-fighting plants" is bogus and misleading. I'll show you what I mean.
Among the compounds that today are regarded as important antineoplastic agents, about 30% occur in nature or are man-made derivatives of substances that occur in nature. Within that 30% there are several discrete classes of compounds, the most important of which are the actinomycins, the anthracyclines, the bleomycins, the epipodophyllotoxins, the taxanes and the vinca alkaloids [note 2].
For the actinomycins, the anthracyclines and the bleomycins, we are indebted to bacteria.
For the epipodophyllotoxins, the taxanes and the vinca alkaloids, we are indebted to plants -- but not to any plants from the tropical rain forests:
To summarize: Among the classes of compounds which are important today as antineoplastic agents, three classes comprise compounds that occur in plants or are man-made derivatives of compounds that occur in plants. None of the plants has come from any tropical rain forest.
It is worth noting that the history of C. roseus and the vinca alkaloids has repeatedly been misrepresented by propagandists. Various advocates for the preservation of the tropical rain forests have used C. roseus as a sort of poster plant and have falsely said that it is a rain-forest organism. Predictably, this deliberate mischaracterization of C. roseus has been parroted in some schoolbooks. See, for example, Terrence M. Gosliner's review of Prentice-Hall Biology in The Textbook Letter for September-October 1990.
Propagandists also have distorted the history of the vinca alkaloids to spin a clever-aborigine tale: The discovery of the alkaloids is ascribed to scientists who received help from Madagascan witch doctors -- witch doctors who, it is implied, had recognized that C. roseus exhibited antineoplastic activity [note 4]. This tale exists in several versions. Here is a version that was distributed in 1991, and was billed as "the famous story of the Madagascar rosy periwinkle," by an outfit called the Tropical Conservation Newsbureau:
Researchers at Eli Lilly pharmaceuticals investigated this low-growing tropical plant with delicate pink blossoms in 1958, following clues from indigenous medicine men, or shamen, in Madagascar.
They found that the plant contained two powerful alkaloids: vinblastine and vincristine. The former was found to be effective against Hodgkin's disease, resulting in an 80 percent remission in sufferers of this form of lymph cancer. Vincristine achieves a 90 percent remission rate against childhood leukemia. . . .
The Newsbureau's "famous story" is a trick. It is an exercise in the use of half-truths and selective omission to create an impression that is false. Here is what is true:
The rosy periwinkle gained the attention of pharmacologists, during the early 1950s, because Madagascan and African indigenes claimed that the periwinkle was useful for treating diabetes. When this claim was tested scientifically, it collapsed: Extracts of C. roseus failed to affect blood-sugar concentrations in experimental animals, and the lore of the indigenes was discredited. However, some of the pharmacologists who did the testing observed that C. roseus extracts markedly suppressed certain types of cells which were implicated in leukemia. Those scientific observations -- not any "clues from indigenous medicine men" -- sparked the research that culminated in the development of vinblastine and vincristine as useful antineoplastic agents. Madagascan witch doctors were not in the picture anywhere.
The similarity between the Newsbureau's "indigenous medicine men" disinformation and Holt's "native people" disinformation is obvious and needs no further comment.
William J. Bennetta is a professional editor, a fellow of the California Academy of Sciences, the president of The Textbook League, and the editor of The Textbook Letter. He writes often about the propagation of quackery, false "science" and false "history" in schoolbooks.
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