Fever: Blessing or Curse?

TO THE EDITOR:

In his article [1], Dr. Mackowiak tries to explain why a human would evolve to develop a sometimes beneficial, other times harmful trait such as fever. He argues that one way to approach the concept is to understand evolution at the species level rather than at the individual level. Thus, a person prematurely killed by a high fever may not benefit from the fever, but other members of the species, who will no longer be exposed to the illness, will benefit (a sort of evolutionary altruism).

The problem with this explanation is that most evolutionists, including Darwin, have argued that in almost all cases, evolution occurs at the level of the individual. As Stephen Jay Gould [2] points out:

Most evolutionists would now admit that group selection can occur in certain special situations (species made of very many discrete, socially cohesive groups in direct competition with each other). But they regard such situations as uncommon if only because discrete groups are often kin groups, leading to a preference for kin selection as an explanation for altruism within the group.

In other words, suppose I die of a fever in a way that allows my siblings to live. My death will have promoted the ongoing life of individuals who share many of my genes. In that respect, whatever genetic trait caused me to die altruistically will (to the extent that my siblings share the trait) be passed on to future generations, as will many of my genes. This altruism, then, is not evidence of evolution at the species level but at the individual level. My death has served to pass on some amount of my genetic information. Suppose, instead, that my act of altruism saves the lives of persons unrelated to me. What will then happen to my genes? Because I have died, I no longer have a chance to pass on my genes. And because people unrelated to me are unlikely to share this gene, the gene that caused my altruism will not be propagated. Instead, others who do not have the gene will survive, and their genes will be propagated. Evolution is generally not altruistic.

Perhaps a simpler explanation could be applied to the evolution of fever. Fever sometimes hurts, but more often it helps. Thus, one is more likely to survive (and pass on one's genes) if one can mount a fever than if one cannot. Evolution is not a perfect process. Sickle cell disease exists because it more often helps persons in areas where malaria is common than it hurts them. Why should fever be any different?

• Copyright ©2004 by the American College of Physicians