levels.
It became clear in the 1970s that low iron levels associated with disease could be helpful, not harmful, but even now, Kluger and his associates find that only 11 percent of physicians and 6 percent of pharmacists know that iron supplementation may harm patients who have infections. Although the sample was small, the study illustrates the difficulty of making clinicians aware of some established scientific findings. Even top researchers may neglect to mention this adaptive mechanism. A recent study in
The New England Journal of Medicine
showed that children with cerebral malaria were more likely to recover if they were treated with a chemical thatbinds iron, but the article did not describe the body’s natural system for binding iron during infection. The evolved mechanism that regulates iron binding is but one specific illustration of the broader principle that we should be careful to distinguish defenses from other manifestations of infection, slow to conclude that a bodily response is maladaptive, and cautious about overriding defensive responses. In short, we should respect the evolved wisdom of the body.
S TRATEGIES AND C OUNTERSTRATEGIES
M edical researchers are not the only ones who deal with conflicts between organisms. Ecologists and animal-behavior specialists routinely deal with predator-prey relationships, struggles between males for mating opportunities, and many other sorts of conflict. They recognize the evolutionary significance of the phenomena they observe and use such terms as
strategy
and
tactic, winner
and
loser
, and other indications of commitment to the adaptationist program. This approach has been richly rewarding for ecologists and others who are steeped in Darwinism. A similar approach to phenomena such as fever ought to be similarly rewarding in a field of such vital interest to all of us.
The contest between parasites and their hosts is a war, and every sign and symptom of infection can be understood in relation to the underlying strategies of one or the other belligerent. Some, like fever and iron withholding, benefit the host (defenses); others benefit the pathogen; and a few are incidental effects of the war between them. The strategies are not, of course, products of conscious thought, but they are strategies nonetheless. Bacteria that sneak into the body by pretending to be harmless are rather like Greek soldiers hiding in a wooden horse. When the manifestations of infection are related to conflicting interests, they fit neatly into categories based on their functional importance. Table 3-1 gives an overview of these categories and a guide to the organization of this chapter.
T ABLE 3-1 A C LASSIFICATION OF P HENOMENA A SSOCIATED WITH I NFECTIOUS D ISEASE
O BSERVATION
E XAMPLES
B ENEFICIARY
Hygienic measures taken by host
Killing mosquitoes, avoiding sick neighbors, avoiding excrement
Host
Host defenses
Fever, iron withholding, sneezing, vomiting, immune response
Host
Repair of damage by host
Regeneration of tissues
Host
Compensation for damage by host
Chewing on other side to avoid tooth pain
Host
Damage to host tissues by pathogen
Tooth decay, harm to liver in hepatitis
Neither
Impairment of host by pathogen
Ineffective chewing, decreased detoxification
Neither
Evasion of host defenses by pathogen
Molecular mimicry, change in antigens
Pathogen
Attack on host defenses by pathogen
Destruction of white blood cells
Pathogen
Uptake and use of nutrients by pathogen
Growth and proliferation of trypanosomes
Pathogen
Dispersal of pathogen
Transfer of blood parasite to new host by mosquito
Pathogen
Manipulation of host by pathogen
Exaggerated sneezing or diarrhea, behavioral changes
Pathogen
How can a host guard against infection? First, it can avoid exposure to pathogens. Second, it can erect barriers to keep them out of the body and act quickly to defend and repair any breaches in the defenses. If pathogens do get beyond the outer ramparts, it can flag any cells that lack proof of
It became clear in the 1970s that low iron levels associated with disease could be helpful, not harmful, but even now, Kluger and his associates find that only 11 percent of physicians and 6 percent of pharmacists know that iron supplementation may harm patients who have infections. Although the sample was small, the study illustrates the difficulty of making clinicians aware of some established scientific findings. Even top researchers may neglect to mention this adaptive mechanism. A recent study in
The New England Journal of Medicine
showed that children with cerebral malaria were more likely to recover if they were treated with a chemical thatbinds iron, but the article did not describe the body’s natural system for binding iron during infection. The evolved mechanism that regulates iron binding is but one specific illustration of the broader principle that we should be careful to distinguish defenses from other manifestations of infection, slow to conclude that a bodily response is maladaptive, and cautious about overriding defensive responses. In short, we should respect the evolved wisdom of the body.
S TRATEGIES AND C OUNTERSTRATEGIES
M edical researchers are not the only ones who deal with conflicts between organisms. Ecologists and animal-behavior specialists routinely deal with predator-prey relationships, struggles between males for mating opportunities, and many other sorts of conflict. They recognize the evolutionary significance of the phenomena they observe and use such terms as
strategy
and
tactic, winner
and
loser
, and other indications of commitment to the adaptationist program. This approach has been richly rewarding for ecologists and others who are steeped in Darwinism. A similar approach to phenomena such as fever ought to be similarly rewarding in a field of such vital interest to all of us.
The contest between parasites and their hosts is a war, and every sign and symptom of infection can be understood in relation to the underlying strategies of one or the other belligerent. Some, like fever and iron withholding, benefit the host (defenses); others benefit the pathogen; and a few are incidental effects of the war between them. The strategies are not, of course, products of conscious thought, but they are strategies nonetheless. Bacteria that sneak into the body by pretending to be harmless are rather like Greek soldiers hiding in a wooden horse. When the manifestations of infection are related to conflicting interests, they fit neatly into categories based on their functional importance. Table 3-1 gives an overview of these categories and a guide to the organization of this chapter.
T ABLE 3-1 A C LASSIFICATION OF P HENOMENA A SSOCIATED WITH I NFECTIOUS D ISEASE
O BSERVATION
E XAMPLES
B ENEFICIARY
Hygienic measures taken by host
Killing mosquitoes, avoiding sick neighbors, avoiding excrement
Host
Host defenses
Fever, iron withholding, sneezing, vomiting, immune response
Host
Repair of damage by host
Regeneration of tissues
Host
Compensation for damage by host
Chewing on other side to avoid tooth pain
Host
Damage to host tissues by pathogen
Tooth decay, harm to liver in hepatitis
Neither
Impairment of host by pathogen
Ineffective chewing, decreased detoxification
Neither
Evasion of host defenses by pathogen
Molecular mimicry, change in antigens
Pathogen
Attack on host defenses by pathogen
Destruction of white blood cells
Pathogen
Uptake and use of nutrients by pathogen
Growth and proliferation of trypanosomes
Pathogen
Dispersal of pathogen
Transfer of blood parasite to new host by mosquito
Pathogen
Manipulation of host by pathogen
Exaggerated sneezing or diarrhea, behavioral changes
Pathogen
How can a host guard against infection? First, it can avoid exposure to pathogens. Second, it can erect barriers to keep them out of the body and act quickly to defend and repair any breaches in the defenses. If pathogens do get beyond the outer ramparts, it can flag any cells that lack proof of
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