Monday, July 18, 2011

What You Don’t Know About Evolution Can Kill You

As noted in a previous blog entry, evolution can occur rapidly. Perhaps the best example of how rapidly natural selection can work is the evolution of resistant organisms, such as antibiotic-resistant bacteria. A mutant bacterium that has the ability to resist penicillin will thrive in the body of a person who is taking penicillin. This is because the penicillin has wiped out the bacteria that cannot resist it. The result is a person who is carrying around a culture of resistant bacteria. These bacteria can then spread to other people. This occurs readily when humans are in close contact, such as in hospitals, or overcrowded prisons, or schools. This same mutant bacterium, in the absence of antibiotics, is inferior to the non-resistant bacteria.

Humans have developed many kinds of antibiotics. But for each of these antibiotics, there are populations of bacteria somewhere that have evolved resistance to them. Fortunately, not all bacteria have evolved resistance to all antibiotics. But some populations of bacteria, called “superbugs,” have evolved resistance to several kinds of antibiotics. Many of you, like me, have known someone who became ill or died from a resistant bacterial infection that they acquired in a hospital or nursing home.

It takes only a few years for populations of bacteria to evolve resistance to any particular kind of antibiotic, and it has taken only a few decades for resistance to antibiotics in general to become a major public health problem. Many viruses, such as HIV, have evolved resistance to antiviral medications as well.

In a similar fashion and almost as rapidly, populations of insects have evolved resistance to pesticides used to control them. There are many populations of insects, many of which spread diseases from one human to another, which will no longer die if you spray them. There are populations of disease-carrying rats that cannot be killed by rat poison. Environmentalist Rachel Carson pointed out in 1962 that the overuse of pesticides not only polluted the environment but also proved ultimately useless because of evolution: “If Darwin were alive today the insect world would delight and astound him with its impressive verification of his theories of the survival of the fittest. Under the stress of intensive chemical spraying the weaker members of the insect populations are being weeded out. Now, in many areas and among many species only the strong and fit remain to defy our efforts to control them.”

In all these ways, from the evolution of antibiotic-resistant bacteria to the evolution of pesticide-resistant vermin, agricultural and medical researchers (some of whom are creationists) have had to take evolution into account when developing strategies to control the spread of infectious diseases and pests. Germs and disease vectors are moving targets, and evolution is the reason for this. Evolution happens in hospitals (and down on the farm, too) not over the course of millions of years but over the course of just a few months. What you don’t know about evolution can kill you.

This entry appeared in my book Life of Earth: Portrait of a Beautiful, Middle-Aged, Stressed-Out World, from Prometheus Books.

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