Viral evolution is in the news because scientists reportedly created a new strain of bird flu (H5N1) that's highly contagious, prompting a government advisory board to request that scientific journals not publish the details.
As I quizzed Penn bioterrorism expert Harvey Rubin about the situation, he continued to talk about evolution and "fitness" of flu viruses. Indeed, he said, the whole point of creating a newer, scarier H5N1 was to help anticipate the virus' future evolution.
It's not easily transmissible now. But thanks to evolution, that might change.
This conversation led me to biologist Eddie Holmes of Penn State's Center for Infectious Disease Dynamics. "Viruses give us the best, most precisely defined examples of evolution you could possibly think of," he said.
Flu viruses evolve particularly fast because they're based on RNA - the single-stranded relative of DNA. RNA doesn't have any mechanism by which to repair copying errors, the way DNA does, so these viruses mutate much faster than DNA viruses.
Working with viruses, Holmes said, "is like watching human evolution on fast-forward." In 10 years, a virus can undergo as much evolution as a human could in 10 million.
The fact that these viruses undergo mutations is just part of the story. Their mutated progeny are subject to the sorting effect of natural selection. Those that are best at surviving and reproducing themselves predominate.
Viruses have hit upon a number of survival strategies, said Holmes. Measles infects children, thus ensuring a constant crop of new potential hosts. Herpes viruses can lie low, going undetected by the immune system much of the time, so it can survive in a host and spread for decades.
