Why We Get Sick (40 page)

“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.

W
e have said before, but here repeat, that moral principles cannot be deduced from biological facts. For instance, the knowledge that aging and death are inevitable has no direct implications for how much of our medical dollar we should spend on the very elderly. Facts can, however, help us to achieve whatever goals we decide to strive for. The current crisis in funding and organization of health care in the United States comes from several sources, including new funding mechanisms, new technology, other economic changes, and social values that increasingly condemn gross differences in the quality of health care. In a system this complex, no general policies will please everyone, and it may not be possible to implement the best available policies because of the power of politics.

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.

F
ew 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.

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).

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 clutch-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).

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).

2
The sequestration of iron as a defense against bacterial pathogens is discussed by E. D. Weinberg in
Physiological Reviews
, 64:65–102 (1984). The treatment of malaria with iron chelating agents is reported by V. Gordeuk et al. in
The New England Journal of Medicine
, 327:1473–7 (1992).

3
For a wide-ranging review of progress in bringing evolution to bear on microbiology, see
Parasite-Host Associations: Coexistence or Conflict
, edited by C. A. Toft et al. (New York: Oxford Univ. Press, 1991). A still-valuable general review of host-parasite coevolution is P. W. Price’s
Evolutionary Biology of Parasites
(Princeton, N.J.: Princeton Univ. Press, 1980).

4
Behavioral defenses against parasites are discussed by B. L. Hart in
Neuroscience and Biobehavioral Reviews
, 14:273–94 (1990). The functions of pain and the shortened lives of those who lack it are described by Ronald Melzack in
The Puzzle of Pain
(New York: Basic Books, 1973).