As the Zika virus continues to spread — now to more than 20 countries throughout the Americas — so too does the pressure to act. What compels our action is clear: The Zika virus is associated with, and seems the cause of, a surging number of cases of microcephaly, a birth defect in which babies have small heads and underdeveloped brains. Strategies being considered to reduce the Zika threat include reducing populations of the primary vector of the virus, mosquitos. Although multiple techniques are available, some groups are calling for widespread reintroduction of the pesticide DDT. However, DDT was banned in the U.S. in 1972 and strongly discouraged for use throughout the world in the Stockholm Convention of 2001. Advocates for DDT exemplify a common reaction to urgent human need: acting quickly without careful consideration of the long-term consequences. We are especially prone to this response in fearful situations, when human suffering is visible and pronounced.
But let's take a closer look at the potential outcomes of this narrow and shortsighted approach to the Zika virus. DDT is known to adversely affect human health, including the liver, nervous system and reproduction. It is listed as a possible human carcinogen and can linger in the soil for hundreds of years. From an ecological standpoint, DDT has been the poster child for "biomagnification" — a phenomenon in which fat-soluble toxins accumulate in animal tissues and reach dangerous levels as they move up the food chain, affecting a wide variety of animals, including humans. This is the reason is why DDT nearly caused the extinction of charismatic birds like the peregrine falcon, bald eagle and brown pelican.
Even the American Mosquito Control Association cautions against using DDT, explaining that mosquito-breeding hotspots in cities (e.g., old tires, small containers) are not as amenable to spraying as agricultural ditches. The association also notes that past use of the pesticide has resulted in widespread DDT resistance in mosquito populations and future use may also result in resistance to safer pesticides too. So, while the need to act is clear, it is even clearer that a careful review of strategies to reduce Zika risk is needed, and that several alternatives exist that may be more effective, without the weighty human health and ecological burdens of DDT.
Of course, Zika is not the only example of a knee-jerk reaction to urgent human need. History shows, again and again, that acting on our instincts often results in dire unintended consequences. In his 1936 paper, sociologist Robert Merton identified several routes to unintended consequences. Chief among them is ignorance, wherein we simply lack the knowledge to anticipate bad outcomes. We also make mistakes due to incorrect appraisals of situations, the available choices about a course of action, or about their implementation. One particularly common error is to falsely assume that past actions will continue to produce desired outcomes. An insidious problem also arises via the immediacy of interest, wherein a decision-maker's focus on the immediate consequences causes a failure to consider the full range of consequences and, potentially, preferable alternatives that better achieve long-term goals. Like your grandmother may have said, "look before you leap."
Consider the "Four Pests" campaign of Mao Zedong's China during the Great Leap Forward from 1958 to 1962. Mao sought to improve hygiene and increase crop yield by controlling rats, flies, mosquitos and grain-eating sparrows. The result? Bird populations crashed, but because those same birds also consumed large numbers of crop-eating insects, crops were decimated by insect pests and mass starvation ensued. The first Green Revolution offers another example. By promoting agricultural intensification and industrialization, global yields improved, but per capita hunger also increased in some regions because the high cost of seeds and other crop inputs (e.g., fertilizers, pesticides) forced smallholder farmers out of agriculture and into urban slums. The Green Revolution also had far-reaching environmental consequences, including pollution, depletion of soil nutrients and loss of biodiversity.
We continue to stumble into similar unintended consequences today. After the 2006 outbreak of E. coli in packaged spinach killed three humans and sickened hundreds of others in the U.S., the practice of removing non-crop vegetation (e.g., hedgerows and trees) around agricultural fields was widely implemented to create a buffer that would discourage wildlife and domestic animals from entering and potentially contaminating fields. However, recent research shows that removing non-crop vegetation has the opposite effect. Rather than reducing pathogen presence, vegetation removal increased presence of E. coli and salmonella. Moreover, the practice may even be harmful to farms by reducing insect populations that pollinate many crops.
Likewise, concern over climate change and rising sea levels has led some island communities to react by building sea walls, thereby destroying coral reefs and coastal marshes and wetlands. Ironically, removing those natural ecosystems may actually increase vulnerability to rising waters and storms and reduce the resiliency of human communities to climate change. What's more, by imperiling fisheries and dampening tourism, these approaches can also deplete resources that offer critical support to local economies.
Of course we cannot act with perfect knowledge; there will always be some errors and missteps. However, we must recognize that our health and well-being are inextricably linked to healthy, functioning ecosystems. We must acknowledge that rash decisions made with limited attention to the long-term are very likely to produce unintended and often undesirable outcomes.
Rodewald is director of conservation science at the Cornell Lab of Ornithology, professor in the Department of Natural Resources at Cornell University, faculty fellow at Cornell University's Atkinson Center for a Sustainable Future, and a Robert F. Schumann Faculty Fellow. Views expressed in her column are hers alone and do not represent those of these institutions.