DDT, Malaria, and the Environment--Posner's Comment
I am a strong environmentalist, and support the ban on using DDT as a herbicide. Although Rachel Carson's belief that DDT causes cancer has not been substantiated, there seems little doubt that its widespread use as a herbicide, if continued, would have caused a significant reduction in biodiversity because of its lethal effect on many fish and bird species. In my book Catastrophe: Risk and Response 63 (2004), I quote a responsible estimate that the combined effect of human population growth (and resulting contraction in animal habitats), herbicide use, global warming, and other factors is causing 10,000 species to become extinct every year. Of course, there have always been extinctions--without which there would be no room for new species to evolve--but the fossil record suggests that the background (i.e., pre-human) average annual number of extinctions is only one. Even the fierce environmental skeptic Bj√∏rn Lomborg estimates that the current annual extinction rate is 1500 times the background rate. And these figures greatly understate the loss of genetic diversity, because much genetic diversity is intraspecies (e.g., birds of the same species but a different color; or imagine if there were only one breed each of dogs and cats). That diversity has been plummeting as well, in part because of selective breeding, which reduces the number of strains of each crop to the best, the others being abandoned.
The decline in genetic diversity--to which spraying crops with DDT would be contributing significantly if it were permitted--is alarming even from a purely selfish anthropocentric perspective because such diversity, like other forms of diversification, performs an important insurance function. This is most obvious when one considers plant diversity; if there were only one strain of wheat, predator evolution would concentrate on it and once the strain was eliminated a significant part of the human food supply would be destroyed. But with animals too, the elimination of a species (or even a breed) can have a ramifying effect throughout the food chain, as when the exctinct species was the major food source of another species, which in turn was a major food source of still another species, and so on.
All this said, the quantities of DDT used in spraying indoor houses in Subsaharan Africa (where 90 percent of malaria deaths occur) are so minute that the environmental effects are inconsequential. The Stockholm Convention on Persistent Organic Pollutants (2001) bans DDT but with an exception for its use against malaria, and the puzzle is why the exception is so rarely invoked, South Africa being a notable exception. An even greater puzzle is why the Bill and Melinda Gates Foundation, which is the world's largest foundation and has made the eradication of malaria a priority, is spending hundreds of millions of dollars searching for a vaccine against malaria but nothing (as far as I know) to encourage indoor spraying with DDT. Of course, spraying can't eradicate malaria, because it just kills malaria-bearing mosquitoes that happen to get inside a house, but it appears to be extremely effective in minimizing malaria infection, as well as being cheap. So it is difficult to understand why the Gates Foundation doesn't divert some of its resources to promoting and if necessary financing the spraying, pending the discovery of a vaccine. As we know in the case of AIDS, the search for a vaccine against a particular disease can be protracted.
Not that eliminating childhood deaths from malaria (I have seen an estimate that 80 percent of malaria deaths are of children) would be a completely unalloyed boon for Africa, which suffers from overpopulation. But on balance the case for eradicating malaria in Africa, as for eradicating AIDS (an even bigger killer) in Africa, is compelling. Malaria is a chronic, debilitating disease afflicting many more people than die of it, and the consequence is a significant reduction in economic productivity.
Considering how much cheaper and easier it would be to (largely) eliminate malaria than to eliminate AIDS (which would require behavioral changes to which there is strong cultural resistance in Africa), the failure of the African countries, the World Health Organization, the World Bank, and private foundations and other nongovernmental organizations to eliminate most malaria by means of indoor spraying with DDT is a remarkable political failure.