J. B. S. Haldane (1949) on infectious disease and evolution.

CHARLES Darwin was gratefully aware of the adFisher and Luca Cavalli-Sforza, but there is scant record vances in microbiology and infectious disease (ID) of their interventions. associated with his contemporaries, Louis Pasteur and In his paper, Haldane recites common knowledge of Robert Koch. Nevertheless, in none of his works does ID and its potential potency as an agent of natural seleche make substantial mention of the role of ID as a tion. His most pungent remark was, “It is much easier driving force in natural selection. In contemporary obfor a mouse to get a set of genes which enable it to servation, this seems self-evident, with frequent decimaresist Bacillus typhimurium than a set which enable it to tion of species by ID: viruses, bacteria, protozoa, or resist cats.” That may well be; he overlooks the unfungi. With rare exceptions, the paleontologists have matched evolutionary potential of the bacilli, which remained as oblivious as Darwin, but the evolutionary guarantees this will be an unending contest. responses to ID leave few qualitative marks on the fossil A special feature of ID is its density dependence, and record. We can only speculate how many faunal extincHaldane looks to it as the ultimate restraint on populations may have stemmed from ID panzootics. We must, tion size. Noting Stalker’s parlous efforts to cultivate of course, marvel at the intricacies of the immune defenScaptomyza in the laboratory, as an alternative to Drosive systems that have evolved to keep pace with microsophila, he predicts that the Drosophila industry will bial invasion. As far as current knowledge informs us, succumb when it gets too large. This prevision was half these are remarkably uniform among vertebrates, and right if we give it credit as an anticipation of the global their main outlines were laid down 200 million years spread of P elements in laboratory cultures. As with ago. However, we still have a long way to go in tracing many other “parasites,” the nuisance they bring is at least the adaptations that may distinguish species that enable partly compensated for by new insights they provoke. rodents and carrion eaters to pursue a lifestyle that In a more subtle argument, Haldane points to ID as deters humans and felines. an accelerator of speciation. Briefly summarized, this Fifty years ago, J. B. S. Haldane (1949) published a occurs when each parasite foments a specialized ecologispeculative review that is now often cited as inspiring cal niche, namely resistance to it. new thinking about disease and evolution. Its original With few exceptions, Haldane brought no experimenvenue was a supplement to La Ricerca Scientifica, retal data of his own to the discussion, and this was the cording the papers from a “Symposium on Ecological case here. He was, however, well acquainted with the and Genetic Factors in Speciation Among Animals.” established polymorphisms of blood group factors and This was organized by Adriano Buzzati-Traverso and other antigens, and he assumed these were driven as held at the Istituto Sieroterapico Milanese. Among the adaptations to still unidentified ID. He also cited examfew recent citations to any other papers presented there ples from phytopathology, the Puccinia (rusts) infecting were a handful referring to Helen Spurway and Th. wheat, and the participation of specific genes. He was Dobzhansky. But Dobzhansky (1951) did not refer to probably also likely aware of the work initiated at the the Haldane paper in his Genetics and the Origin of Species Rockefeller Institute on rat strains resistant to Salmo(Ed. 3). Others present at the Symposium included R. A. nella infection (Irwin and Hughes 1933) and of Gowen’s (1952) studies on mice. While these and many other works had affirmed widely held intuitions that genetic constitution plays an important role in response Author e-mail: [email protected]