LETTER
Fever: Blessing or Curse?
Eric Schwam, MD
15 December 1994 | Volume 121 Issue 12 | Pages 982-984
TO THE EDITOR:
Although I agree with Dr. Mackowiak [1] that it is useful to view biological processes such as fever from an evolutionary perspective, his hypothesis is based on a misunderstanding of the process of evolution by natural selection. His assumption that the essence of evolution is "preservation of the species rather than the survival of the individual" has no basis in evolutionary theory.
Genes are "selfish" [2]. Their sole "purpose" is to make copies of themselves. If a gene's phenotype confers a survival advantage that allows an individual to reproduce, then more copies of the gene are produced. Genetically determined altruistic behavior is seen only when it benefits related individuals who are likely to carry the same gene. Thus, a gene may reduce an individual's survival if it sufficiently increases the survival of other individuals carrying the same gene. Such sacrifices are not made for "the species." If the first genes for fever decreased infection-related mortality, they would have been perpetuated through natural selection. If, however, they increased infection-related mortality for the individual but reduced contagion and subsequent mortality for unrelated individuals, these genes would not receive the benefit of natural selection.
It is not necessary for a biological system such as fever to be adaptive in all situations for it to be evolutionarily advantageous. For example, when the genes for the renin-angiotensin system first appeared, they were presumably selected because of their adaptive responses to extracellular volume depletion (for example, from infectious diarrhea or acute traumatic blood loss) in individuals who could still reproduce. Fluid retention is, of course, maladaptive in cardiac dysfunction when it results in pulmonary congestion and hypoxemia. Few individuals experience congestive heart failure before or during their reproductive years, so no evolutionary survival disadvantage results from the maladaptation. Thus, biological processes such as fever or the renin-angiotensin system can be adaptive in certain circumstances and maladaptive in others and remain evolutionarily advantageous.
1. Mackowiak PA. Fever: blessing or curse? A unifying hypothesis. Ann Intern Med. 1994; 120:1037-40.
2. Dawkins R. The Selfish Gene. New York: Oxford University Press; 1976.
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