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The Escape of the Pathogens: an evolutionary arms race

Flu virusHuman populations are constantly locked in evolutionary arms races with pathogens that invade our bodies. We must recognize that these pathogens (such as the flu virus shown at right) are continuously evolving entities in order to develop better ways to fight them and control their evolution.

An ounce of prevention…every year?
Recently, the mayor of New York City called upon citizens to get a head start on one particular evolutionary arms race: “I urge older New Yorkers and others at risk to protect themselves from flu and pneumonia through a simple and proven ounce of prevention: immunizations. The time to get immunized is now, before the peak of the flu season.”

Many of those New Yorkers had already gotten flu shots the year before and the year before that, but, perhaps strangely, they were being asked to get yet another immunization. Why do we need a new flu shot every year? Can’t modern medicine invent just one vaccine that would do the trick?

Researcher looking into a microscopeFlu viruses evolve rapidly.
As they circulate through populations around the world and switch hosts, flu viruses change so much that our vaccines are rendered obsolete every year. The flu is a problem for which a solution must be redesigned and rebuilt every year, like a bridge that gets washed away every flood season. Only by understanding the flu as an evolving entity can we understand why our solution to the problem must change every year.

Every day we come into contact with millions of bacteria and viruses. Some are harmful and others are beneficial, while the rest have no apparent effect on our health. When harmful microorganisms enter our bodies, a battle ensues.

Rapid reproduction and natural selection
Because bacteria and viruses reproduce rapidly, they evolve rapidly. These short generation times — some bacteria have a generation time of just 15 minutes — mean that natural selection acts quickly. In each pathogen generation, new mutations and gene combinations are generated that then pass through the selective filter of our drugs and immune response. Over the course of many pathogen generations (a small fraction of a single human lifetime), they adapt to our defenses, evolving right out from under our attempts to rid ourselves of them.

Applying our knowledge of evolution
But that doesn’t mean that we should stop trying to win these battles. By understanding these pathogens as evolving entities, subject to the same processes of evolution that we can study in fruit flies or the fossil record, we may be able to identify ways to slow their progress.

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