Gone Fishing: Mosquitoes, Malaria

In the summer I eat fewer bananas and catch more fish. I cut down on fruit that seems to make me more attractive to the mosquitoes that inhabit wetlands near my favorite trout streams. It’s folk wisdom, and it may be proven false by science, but as with the flies I tie on the end of my tippet, my belief is the critical factor. I think that fewer bananas (and more garlic) renders me relatively unattractive to blood sucking insects, and so the evidence of my experience bears me out.

In the winter I do more angling in the library than along streams. There I recently netted an article of interest on the introduction of malaria in the New World: Corinne Shear Wood, “New Evidence for a Late Introduction of Malaria into the New World,” Current Anthropology 16 (March 1975), 93-104. Wood’s abstract at the end of the article sums the argument.

The unique, overwhelming group-O frequency present among indigenous American populations is seen as a result of mother-child ABO incompatibility effects operating in the absence of the positive selection pressures by malaria vectors favoring enhanced survival for genes A and B that the investigation findings suggest. It is proposed that had malaria been present to act upon the original gene pool, a balanced ABO polymorphism would be found in the New World Indians today.
Wood, “New Evidence,” 5.

Comment by sixteen scholars follow Wood’s article, taking up more pages than her report. There are several criticisms that urge caution in reasoning from her preliminary results, and most suggest the need for further studies. None of them fault her assessment of the historical literature up to the time of her study. It had been inconclusive, but was leaning toward Old World origins.

There should be no doubt from the responses, and her reply, that her study does more to raise questions than offer answers. As the article was published more than thirty years ago, we might expect to find corroborating or refuting evidence by now.

A much more recent study brought to my attention by John Hawks offers a conclusion supporting at least one aspect of Wood’s contentions, that malaria could have impacted selective pressure regarding blood groups:

This work provides insights into malaria pathogenesis and suggests that the selective pressure imposed by malaria may contribute to the variable global distribution of ABO blood groups in the human population.
J. Alexandra Rowe, et al, “Blood group O protects against severe Plasmodium falciparum malaria through the mechanism of reduced rosetting,” Proceedings of the National Academy of Sciences 104 (October 2007), 17471-17476.

In addition, some genetic analysis published a few years ago, also inconclusive, leans towards origins of malaria in Africa. See Jennifer C. C. Hume, Emily J. Lyons, and Karen P. Day, “Archaeology of Epidemic and Infectious Disease,” World Archaeology, 35 (October 2003), 180-192.

This kettle of fish increases skepticism regarding Larry Schweikart’s claim, that “considerable new research in the hard sciences and medicine shows that some diseases thought to be ‘transmitted’ from Europe likely were already here,” if this claim applies to malaria.

I’ve addressed this question from another angle near the end of “America was not a disease-free paradise.” Schweikart and Allen name malaria once, as a New World disease that struck down English colonists that “had no resistance” (A Patriot’s History, 17).