Viruses, explained

I did some simple googling and found the web is rich with explanations about viruses. Huh. Imagine that.

You can start with that video. You can also look further. Like about the evolution of viruses. There’s more below on the evolution of viruses written at a high school or even middle school level. Read more here.


Have you ever wondered why a different strain of flu virus comes around every year? Or how HIV, the virus that causes AIDS, can become drug-resistant?The short answer to these questions is that viruses evolve. That is, the “gene pool” of a virus population can change over time. In some cases, the viruses in a population—such as all the flu viruses in a geographical region, or all the different HIV particles in a patient’s body—may evolve by natural selection. Heritable traits that help a virus reproduce (such as high infectivity for influenza, or drug resistance for HIV) will tend to get more and more common in the virus population over time.[Quick review: What is evolution?]Not only do viruses evolve, but they also tend to evolve faster than their hosts, such as humans. That makes virus evolution an important topic—not just for biologists who study viruses, but also for doctors, nurses, and public health workers, as well as anyone who might be exposed to a virus. (Hint: that means all of us!)

Variation in viruses

Natural selection can only happen when it has the right starting material: genetic variation. Genetic variation means there are some genetic (heritable) differences in a population. In viruses, variation comes from two main sources11start superscript, 1, end superscript:

  • Recombination: viruses swap chunks of genetic material (DNA or RNA).[What are DNA and RNA?]
  • Random mutation: a change occurs in the DNA or RNA sequence of a virus.

We can see variation and evolution of viruses all around us if we know where to look—for instance, in the new flu strains that appear each year.

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