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This colorized negative stained transmission electron micrograph (TEM) image depicts athe A/CA/4/09 swine flu virus in 2009. CREDIT: CDC/C. S. Goldsmith and A. Balish |
Anyone who thinks evolution is for the birds should not be afraid of swine flu. Because if there's no such thing as evolution, then there's no such thing as a new strain of swine flu infecting people.
For the rest of the population, concern is justified.
The rapid evolution of the influenza virus is an example of Nature at her most opportunistic. Viruses evolve by the same means as humans, plus they use tricks such as stealing genetic code from other viruses.
The strategy is what makes the flu so virulent and often keeps the microbes one step ahead of scientists who would destroy or neutralize them.
Pigs to you
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.
David Schaffer, a professor of chemical engineering and bioengineering at the University of California at Berkeley, explains the mechanics of how a flu virus morphs:
"For flu, there are multiple ways that diversity can arise (the virus has multiple strands of RNA in its genome, and it can mix and swap strands with different flu variants to give rise to fully novel variants … in addition, each strand can individually mutate)," Schaffer explained this week.
"Furthermore, in this case, the 'enhanced' property from the virus' point of view is the ability to infect humans. So, this is viral evolution."
But are they alive?
One of the little hole-poking exercises used by critics of evolution is to argue that viruses are not alive. Tell that to the host.
"Viruses may be living or non-living, depending on the definition of life," Deem explained in an email interview with LiveScience. "Viruses + the host (pig or human) are definitely alive. So, this for sure is an example of evolution in the living system of the virus + pig + human."
Schaffer takes a slightly different view:
"Viruses are not alive, in that they do not have the ability to replicate themselves independently, without infecting and relying upon a cell to do so," Schaffer said. "That said, biological entities need not be alive in order to evolve."
And viruses do evolve, swapping new genetic material in and out of their genomes. That's why we can have immunity to a virus we've had in the past, but be wiped out by one our body has never seen before.
The biochemical processes in evolution of a "simpler" biological entity such as a virus are very different from a living organism, Schaffer notes. "However, broadly speaking evolution still always involves two steps, genetic diversification and selection."
At the Understanding Evolution Web site, set up by the University of California Museum of Paleontology and the National Center for Science Education, researchers put it this way:
"To evolve by natural selection, all an entity needs is genetic variation, inheritance, selection, and time, all of which viruses have in spades."
Way sneakier
When humans evolve, the cause is typically random genetic variations that prove beneficial — eventually leading to thumbs for grabbing or brains that process fear impulses more successfully.
Viruses don't have to count on such long odds. They steal DNA that they find useful to their success.
"Many viruses can easily incorporate ready-made genes from other viruses into their genomes," as explained at Understanding Evolution. "This is a possibility anytime a host is infected with two different viral strains."
That's likely what's happened with swine flu.
"It appears the H1N1 swine flu may be a reassortment of the H (hemagglutinin) gene from typical North American pigs with the N (neuraminidase) and M (matrix) genes from European pigs," Deems said. "If so, this new virus is an example of the importance of recombination in evolution. That is, evolution proceeds not only by small mutations of individual DNA or RNA bases, but also by transmission of large pieces of genetic material from one individual to another."
And then what?
Let's say you have a run-of-the-mill flu that's normally transmitted between humans but causes only mild symptoms. Then you also contract a really deadly influenza virus that heretofore was only transmitted between pigs. The two viruses can get together inside you, swap genes, and now you're the host of a newly evolved swine flu virus that can infect your whole family, your colleagues at work, some people at the airport you later fly out of who touch the same armrest you held, and then some folks in the country you fly to. Voila, pandemic!
And it doesn't stop there. Each time another person is infected, the new strain of the virus can grab more genes and mutate further. So if you came from Mexico and infected people in the United States who might have been packing around a different flu, the U.S. swine flu could be different than the Mexican swine flu.
And that's why there's no cure for the flu.
Scientists say it could take six months to develop a vaccine for the new swine flu, and by then, nobody knows what it will have evolved into.
Swine Flu Special Report:
Robert Roy Britt is the Editorial Director of Imaginova. In this column, The Water Cooler, he looks at what people are talking about in the world of science and beyond.
{{ video="LS_090428_pandemic" title="The Truth about Pandemics " caption="Dr. Marc Siegel explains why the term pandemic often inspires more fear than it should, how the media plays on fears, and how governments often make wrong and costly moves." }}
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