How is all this possible? It isn’t. Why set impossible expectations? In part because we naively want our physicians to know everything. Another reason, however, is that no one person is in charge. When a committee decides on the class schedule and every basic science wants more time, the solution is to go on increasing the total amount of class time. Thirty or more hours each week in class is not unusual. After that, the students go home to study their textbooks and notes.
One might think that students’ complaints would lead to reform, but decades of polite complaints changed little. It was technology that finally precipitated some change, technology in the form of the photocopy machine. Instead of going to class, students hire one person to take notes for each lecture, then all of them receive copies. It turns out to be a better survival strategy to stay home and study the notes than to go to class. When only twenty students attend a class for two hundred, professors hit the roof and curriculum reform is born. New attempts are being made, under the strong leadership of some deans, to cut back on the hours, reduce the amount of material, find new ways to transmit it. If these efforts succeed, it will be wonderful indeed.
Such efforts might even make room for Darwinian medicine, except that there are no Departments of Evolutionary Medicine to advocate inclusion of this material and few medical faculty members who know the material and want to teach it. It will take time and further leadership from medical school deans to make room in the medical curriculum for an introduction to the basic science of evolution and its applications in medicine. When evolution is included, it will give students not only a new perspective on disease but also an integrating framework on which to hang a million otherwise arbitrary facts. Darwinian medicine could bring intellectual coherence to the chaotic enterprise of medical education.
CLINICAL IMPLICATIONS
While many clinical implications of an evolutionary view await future research, others can immediately transform the way patients and doctors see disease. Let us listen in as first a pre-Darwinian and then a post-Darwinian physician talk to a patient about gout.
“So, Doctor, it is gout that has my big toe flaming, is it? What causes gout?”
“Gout is caused by crystals of uric acid in the joint fluid. I expect you can imagine only too well how some gritty crystals could make a joint painful.”
“So why do I have it and you don’t?”
“Some people have high levels of uric acid in their systems, probably because of some combination of genes and diet.”
“So why isn’t the body designed better? You would think there would be some system to keep uric acid levels lower.”
“Well, we can’t expect the body to be perfect, now, can we?”
At this point our pre-Darwinian physician gives up on science and dodges the question, implying that such “why” questions need not be taken seriously. Most likely, he or she doesn’t recognize the distinction between proximate and evolutionary explanations, to say nothing of the importance and legitimacy of evolutionary explanations for disease.
The Darwinian physician gives a different answer, one closer to what the patient wanted and was entitled to.
“That’s a good question. It turns out that human uric acid levels are much higher than those of other primates and that uric acid levels in a species are correlated with its life span. The longer-lived the species, the higher the uric acid levels. It seems that uric acid protects our cells against damage from oxidation, one of the causes of aging. So natural selection probably selected for higher uric acid levels in our ancestors, even though some people end up getting gout, because those higher levels are especially useful in a species that lives as long as we do.”
“So high levels of uric acid prevent aging?”
“Basically, that seems to be right. So far, however, there is no evidence that individuals with high uric acid levels live an especially long time, and in any case you don’t want your toe to stay like that, so we are going to go ahead and get your uric acid levels down to the normal range to get the gout under control.”
“Sounds sensible to me, Doc.”
This is not an isolated example. A Darwinian perspective can already assist in the management of many medical conditions. Take strep throat:
“Well, it’s strep all right, so you will need to take some penicillin for seven days,” says the Darwinian physician.
“That will make me better faster, right?” the patient says hoarsely.
“Probably, and it will also make it less likely that you will develop diseases like rheumatic fever because of your body making immune substances that attack the bacteria.”
“But why doesn’t my body know better than to make substances that will attack my own heart?”
“Well, the streptococcus has evolved along with humans for millions of years, and its trick is to imitate the codes of human cells. So when we make antibodies that attack the strep bacteria, those antibodies are prone to attack our own tissues as well. We are in a contest with the strep organism, but we can’t win because the strep evolves much faster than we do. It has a new generation every hour or so, while we take twenty years. Thank goodness we can still kill it with antibiotics, although this may be a temporary blessing. You will do yourself and the rest of the world a favor by taking your antibiotics even after you feel better, because otherwise you may be giving a lift to those variants that can survive short exposures to antibiotics, and those antibiotic-resistant organisms make life difficult for us all.”
“Oh, now I see why I have to take the whole bottle. Okay.”
Or take a patient who has had a heart attack:
“So, Doctor, if my high cholesterol is caused by my genes, what good will it do to change my diet?”
“Well, those genes aren’t harmful in the normal environment we evolved in. If you spent six or eight hours walking around each day to find food, and if most of your food was complex starches and very lean meat from wild game, you wouldn’t get heart disease.”
“But how come I crave exactly the foods you say I shouldn’t eat? No potato chips, no ice cream, no cheese, no steak? You medical types want to take away all the foods that taste best.”
“I’m afraid we were wired to seek out certain things that were essential in small amounts but scarce on the African savannah. When our ancestors found a source of salt, sugar, or fat, it was usually a good idea for them to eat all they could get. Now that we can easily get any amount of salt, sugar, or fat just by tossing things into the grocery cart, most of us eat more than twice as much fat as our ancestors did, and lots more salt and sugar. You are right, it is a kind of a cruel joke—we do want exactly those things that are bad for us. Eating a healthy diet does not come naturally in the modern environment. We have to use our brains and our willpower to compensate for our primitive urges.”
“Well, I still don’t like giving up my favorite foods, but at least that makes it understandable.”
There are a hundred more examples: advice given to a patient with a cold or diarrhea; an explanation of aging; the significance of morning sickness during pregnancy; the possible utility of allergy. While most medical conditions have yet to be explored from an evolutionary view, Darwinian medicine can already be useful in the clinic.
A caveat is necessary. Doctors and patients, like all other people, are prone to extend theories too far. We have lost count of how many reporters have called asking, “So you’re saying we should not take aspirin for a fever, right?” Wrong! Clinical principles of medicine should come from clinical research, not from theory. It is a mistake to avoid aspirin just because we know that fever can be useful, and a mistake not to treat the unpleasant symptoms of some cases of pregnancy sickness, allergy, and anxiety. Each condition needs to be studied separately and each case considered individually. An evolutionary approach does, however, suggest that many such treatments are unnecessary or harmful and that we should do the research to see if the benefits are worth the costs.
PUBLIC POLICY IMPLICATIONS
While not pretending to offer solutions, we observe that the many participants in this debate don’t even agree on what disease is. They know disease is bad but differ wildly on where it comes from and the extent to which it can be prevented or relieved. Some blame faulty genes, others emphasize the amount of disease that results from unfortunate human predilections, especially poor diets and drug use. According to one recent authoritative article, more than 70 percent of morbidity and mortality in the United States is preventable. The article argues strongly for investing in prevention because it will pay off in reduced health care costs. What a terrible irony and frightening harbinger it is that such a noble and practical proposal to improve human health has to be couched as a way to save money! In the light of history, however, this approach is understandable. Again and again, panels of distinguished physicians and researchers have called for prevention instead of treatment. The field of preventive medicine now provides some help, especially in matters of public policy, but people still do not get reliable advice from their physicians about how to stay healthy. New ways of organizing medical care may finally provide incentives for dedicating substantial clinical resources to preserving health based on principles of Darwinian medicine.
PERSONAL AND PHILOSOPHICAL IMPLICATIONS
Few things are as important to us as our health. “How are you?” we ask in greeting each other, the convention of the inquiry still not completely covering its seriousness. “I’ve still got my health,” says the person who has lost everything else. Health is vital. Without it, little else matters. We all want to understand the causes of disease to preserve and improve our health.
Long before there were effective treatments, physicians dispensed prognoses, hope, and, above all, meaning. When something terrible happens—and serious disease is always terrible—people want to know why. In a pantheistic world, the explanation was simple—one god had caused the problem, another could cure it. In the time since people have been trying to get along with only one God, explaining disease and evil has become more difficult. Generations of theologians have wrestled with the problem of theodicy—how can a good God allow such bad things to happen to good people?
Darwinian medicine can’t offer a substitute for such explanations. It can’t provide a universe in which events are part of a divine plan, much less one in which individual illness reflects individual sins. It can only show us why we are the way we are, why we are vulnerable to certain diseases. A Darwinian view of medicine simultaneously makes disease less and more meaningful. Diseases do not result from random or malevolent forces, they arise ultimately from past natural selection. Paradoxically, the same capacities that make us vulnerable to disease often confer benefits. The capacity for suffering is a useful defense. Autoimmune disease is a price of our remarkable ability to attack invaders. Cancer is the price of tissues that can repair themselves. Menopause may protect the interests of our genes in existing children. Even senescence and death are not random, but compromises struck by natural selection as it inexorably shaped our bodies to maximize the transmission of our genes. In such paradoxical benefits, some may find a gentle satisfaction, even a bit of meaning—at least the sort of meaning Dobzhansky recognized. After all, nothing in medicine makes sense except in the light of evolution.
NOTES
Chapter 1. The Mystery of Disease
1 For further discussion of proximate and ultimate (evolutionary) causation, see Ernst Mayr’s The Growth of Biological Thought (Cambridge, Mass.: Belknap Press, 1982) or his brief article “How to Carry Out the Adaptationist Program,” American Naturalist, 121:324–34 (1983). The problem of recognizing and confirming adaptations is dealt with on pp. 38–45 of George Williams’ Natural Selection (New York: Oxford Univ. Press, 1992). A terminological revision is suggested by Paul W. Sherman in Animal Behavior, 36:616–19 (1988).
2 A history of social thought on Darwinism and of political uses of Darwinian metaphors is provided by Carl N. Degler’s In Search of Human Nature: The Decline and Revival of Darwinism in American Social Thought (New York: Oxford Univ. Press, 1991). The inscription on the statue at Saranac Lake is quoted on page 410 of René Dubos’s Man Adapting (New Haven: Yale Univ. Press, 1980).
Chapter 2. Evolution by Natural Selection
1 The Aristotle quotation is from p. 103 of Aristotle: Parts of Animals, translated by A. L. Peck (Cambridge, Mass.: Harvard Univ. Press, 1955).
Two recent books offer superb treatments of the modern concept of evolutionary adaptation. They are Helena Cronin’s The Ant and the Peacock (New York: Cambridge Univ. Press, 1991) and Matt Ridley’s The Red Queen (London, New York: Viking-Penguin, 1993). Cronin’s account is more explicitly historical, with many quotations from Darwin, Wallace, and others. Both can be read with profit by both professional biologists and amateur naturalists.
2 The moth population that quickly evolved a darker color as its background darkened is discussed in many general works on evolution, for instance, on p. 58 of D. J. Futuyma’s Evolutionary Biology, 2nd ed. (Sunderland, Mass.: Sinauer, 1986).
3 Examples of increased reproductive effort causing increased mortality or other costs are summarized on pages 28–9 and 188–93 of S. C. Stearns’s The Evolution of Life Histories (New York: Oxford Univ. Press, 1992).
4 W. D. Hamilton’s classic work is in Journal of Theoretical Biology, 7:1–52 (1964). Any modern book on evolution or animal behavior will discuss Hamilton’s work. Richard Dawkins’s book The Selfish Gene, new edition (Oxford: Oxford Univ. Press, 1989), offers a superb introduction to these ideas. The classic works on reciprocity are by R. L. Trivers in Quarterly Review of Biology, 46:35–57 (1971), and R. M. Axelrod’s The Evolution of Cooperation (New York: Basic Books, 1984). These works are routinely reviewed in modern treatments of animal behavior, such as John Alcock’s Animal Behavior: An Evolutionary Approach, 4th ed. (Sunderland, Mass.: Sinauer, 1989).
5 See E. O. Wilson’s Sociobiology (Cambridge, Mass.: Harvard University Press, 1975) and On Human Nature (Cambridge, Mass.: Harvard Univ. Press, 1978) and Richard Alexander’s Darwinism and Human Affairs (Seattle: University of Washington Press, 1979) and The Biology of Moral Systems (New York: Aldine de Gruyter, 1987).
6 The replay-the-tape-of-life idea is from pages 45–8 of S. J. Gould’s Wonderful Life: The Burgess Shale and the Nature of History (New York: Norton, 1989).
7 The classic study of wing lengths of birds killed by a storm is cited in many recent works, such as John Maynard Smith’s Evolutionary Genetics (New York: Oxford Univ. Press, 1989), which also explains the general topic of selection in favor of intermediate values (normalizing selection). For more on the optimization concept, see G. A. Parker and John Maynard Smith’s article in Nature, 348:27–33 (1990), and The Latest on the Best: Essays on Evolution and Optimality, edited by John Dupré (Cambridge, Mass.: MIT Press, 1987).
8 The term adaptationist program was first used, disparagingly, by S. J. Gould and R. C. Lewontin in their much-cited article “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme,” Proceedings of the Royal Society of London, 6205:581–98 (1979).
9 Gary Belovsky’s work is described in American Midland Naturalist, 111:209–22(1984).
10 For some clear thinking on the clutc
h-size problem and an introduction to recent work, see Jin Yoshimura and William Shield’s article in Bulletin of Mathematical Biology, 54:445–64 (1992).
11 It must be that Darwin and his followers seldom found themselves at stag dances or singles bars, because the obvious minority-sex advantage somehow escaped their notice until it was pointed out by R. A. Fisher on p. 159 of his 1930 book The Genetical Theory of Natural Selection (New York: Dover, 1958 reprint).
12 For very recent work that takes an evolutionary view of disease see G. A. S. Harrison, ed. (1993), Human Adaptation, and The Anthropology of Disease by C. Mascie-Taylor (both Oxford: Oxford Univ. Press, 1994).
Chapter 3. Signs and Symptoms of Infectious Disease
1 The recent understanding of the role of fever in controlling infection is discussed in M. J. Kluger’s article in Fever: Basic Measurement and Management, edited by P. A. MacKowiac (New York: Raven Press, 1990). For an older but still valuable overview, see his Fever, Its Biology, Evolution, and Function (Princeton, N.J.: Princeton Univ. Press, 1979). Data on acetaminophen’s effects on chicken pox are presented by T. F. Doran and collaborators in an article in Journal of Pediatrics, 114:1045–8 (1989). The experiments on fever reduction and the progress of a cold are discussed by N. M. Graham and collaborators in Journal of Infectious Disease, 162:1277–82 (1990). The quotation on p. 28 is from Joan Stephenson in Family Practice News, 23:1, 16 (1993).
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