Living with Microbes

Article excerpt

Human beings have long used antibiotics and other weapons to wage war on microbes. But microbes seem to evolve almost as quickly as scientists devise new means to destroy them. It is time to abandon the war paradigm, the authors argue, and embrace new methods that will allow us a greater measure of peaceful coexistence with microbial life.

In January 2000, nearly two years before terrorists destroyed the World Trade Center and attacked the Pentagon, before anthrax-laden letters spread fear and death through the postal system and the country, the National Intelligence Council warned that naturally occurring infectious diseases were a serious threat to national security and international stability. (*)

This threat is growing worse. In the past 20 years, nearly three dozen deadly microbes have been identified for the first time. These include the viruses that cause hepatitis C, D, and E; the Ebola virus; hantaviruses, which attack the respiratory system; and, most pervasive, the Human Immunodeficiency Virus (HIV). Epidemics of dengue fever, meningitis, influenza, cholera, and other diseases have become increasingly common. One in every 12 people on earth is infected with malaria, in part because the anopheline mosquito has grown increasingly resistant to insecticides and, as an effect of global warming, is now found in areas where it was never seen before. With the emergence of multidrugresistant bacteria and the AIDS pandemic, the tuberculosis mortality rate is rising for the first time in 40 years.

The first new class of antibiotics to be discovered in 30 years has already encountered resistance even though it has not yet been widely used. The same is true for the new antiviral drugs. By 2005, half of all AIDS patients in San Francisco will not respond to any treatment currently available. Mounting evidence implicates bacteria, viruses, and protozoa in an array of conditions and diseases previously thought unrelated to infection: heart disease, rheumatoid arthritis, diabetes, multiple sclerosis, autism, chronic lung diseases, and at least one-quarter of the known varieties of human cancer.

Nonetheless, there is reason for optimism. During the past two decades, evolutionary biologists, microbiologists, and other researchers have begun to learn how and why microbes evolve. In the process, they have found a more effective way of dealing with infectious disease than the old state-of-war, them-or-us approach. This new understanding focuses on our evolutionary relationships with microbes. It tells us that virulence, the harmfulness of a microbial infection, is a product of the evolutionary interplay between microbes and humans. And it shows how we can direct microbial evolution away from infectious disease and toward a more mutually beneficial relationship. In an essay nearly 20 years after his seminal Structure of Scientific Revolutions (1962), Thomas Kuhn wrote that in certain periods "the pieces suddenly [begin] sorting themselves out and coming together in a new way." That is exactly what is going on now.

The evolution of any species requires a population with a diverse gene pool that gives each individual in the species unique characteristics. As Charles Darwin pointed out in Origin of Species (1859), environmental forces favor the survival and reproduction of individuals with certain specific characteristics. Take the human thumb. For our hominid ancestors to develop opposable thumbs, individuals must have appeared whose genes governing the thumb happened to be different, giving them the new ability to hold weapons and tools. This proved a great advantage in surviving in their environment and therefore passing those genes to the next generation. Over time, those without these particular genes evolved in another direction, or died out.

Now turn to the surprising mechanics of microbial evolution. Darwin had no idea of the importance of microbes when he published Origin of Species, but microbes follow Darwinian evolutionary theory very efficiently. …