Last weekend in a post about swine flu, I remarked that the appearance of this virus is a perfect example of rapid evolution in action. Amazingly, this triggered a couple of emails from people denying that viruses evolve, and one comment from a reader who said I was “becoming an extremist” because I pointed out this simple, uncontroversial fact.

Here’s an article at LiveScience on this subject, with statements from other extremists such as bioengineers and wildlife researchers: Swine Flu Is Evolution in Action.

While much of the modern controversy over evolution centers around whether humans evolved from non-human primates (scientists overwhelmingly agree this is the case), some people still try to poke holes in the theory of evolution, one of the most solid theories in science. In addition to evidence from ancient fossils and modern DNA studies, one of the many lines of evidence supporting evolution is that it can quite simply be seen in action among some species that evolve particularly rapidly, such as fruit flies.

But on no stage does evolution unfold more quickly or with more potentially sickening or lethal consequences for humans than among viruses. It is, to pass on a scary phrase used among scientists and marketers, viral evolution. And you could be the star host of this all-too-often deadly show.

The sudden ability of the new swine flu virus to hop from pigs to humans and then to skip from person to person, at least in Mexico, is an excellent example of evolution at work.

“Yes, this is definitely evolution,” said Michael Deem, a bioengineer at Rice University in Texas.

Deem studies how evolution is affected not just by mutations but by the exchange of entire genes and sets of genes. Viruses, which are basically packets of DNA with a protein coat, are really good at this. Viruses are also really good at exploiting the fact that we humans cough and sneeze without covering ourselves and generally don’t wash our hands frequently in a day.

“Viruses have evolved to exploit human contact as a way of spreading,” points out Peter Daszak of the Wildlife Trust, whose team 14 months ago predicted just this sort of evolution in an animal flu, coming from Latin America to the United States after evolving to infect people.