VIRUSES: DO THEY EVOLVE?

I have read on a creationism website "we don't see evolution happening in our world today." Of course we do! Consider flu viruses. Every new outbreak of flu is a new virus. Is this not evolution? – Ellen S.

Thank you very much for your question. In order to answer it, we will have to delve into the world of microbiology and natural selection. But first we need to discuss the two main subjects in your question: evolution, and viruses.

 Viruses are a bit of a puzzle for microbiologists. They contain DNA and RNA that are found in all living things. This is packaged up in a “protein coat”. Despite this, viruses are not usually considered to be living because they are not made up of cells and cannot reproduce by themselves. Instead, the viruses will inject DNA or RNA into a living cell, hijack the reproductive organelles of the cell, make copies of the DNA/RNA, and then assemble them so they can spread. Viruses differ considerably in their ability to cause disease. Many known viruses are not associated with disease at all. Others cause very mild symptoms that often go undetected. And some, such as the HIV virus that causes AIDS in people appear to have come from another species where they do not cause disease. And of course, there is the infamous influenza virus, which I am currently suffering from as I write this!

We now need to discuss evolution. It is important to recognise that biologists use several distinct definitions for evolution that are blurred together as if they are all the same. Evolution means “change” and can be used to describe an animal changing slightly to show different traits, or it can be used to describe molecules changing into humans over billions of years. The two different types of evolution are called macroevolution, and microevolution. But aren’t they both the same? Over vast periods of time, can the small changes in an animal build up into large, new traits? No. Microevolution is limited to the genetic information it contains within the DNA of an organism. This information can be dominant or recessive, in other words, switched on, or switched off. Take, for instance, a dog. In its DNA, there may be information for long and short hair. In this particular dog, both are dominant (switched on). So the dog has medium hair. Now that dog has babies, and passes on her hair genes. In these new dogs, the short hair is dominant. The genes for long hair may be switched off, or, if the mother and father did not give any long hair genes, they may not even possess the genes for long hair. Later, the mother has more puppies, this time with the long hair gene dominant. Again, the short hair gene may be either switched off, or not even present. Now the dog pack move from their location, to a hot climate (Africa?). Now this is where natural selection begins.

The famous natural selection statement “Survival of the Fittest” has an opposite statement: “Extinction of the Unfit”. In this warm climate, the long haired dogs will be naturally selected against – i.e. they will die from overheating.

Macroevolution (molecules to man evolution) is entirely different. This describes the changes in an animal kind over time. This means that new traits are added that the organism didn’t come from its genes. In other words, new information has to be added to the DNA genome. As of yet, we have found no natural means of creating new information in the DNA.

So what about viruses? They seem to change, and a new virus epidemic occurs. Is this evolution? No. Instead something very similar to our dog examples is happening.

Viruses can change in several different ways to render immune systems and antibiotics useless, and create a new epidemic, without any evolution involved. The most important way a virus can do this is by a process called “re-assortment”. This occurs when two varieties of virus infect the same host. When viruses infect cells, the virus is effectively disassembled and then re-made. If two viruses affect one cell, genes from each virus can be mixed up during the reassembly process. Take, for instance, the animal viruses that are commonly heard about on the media. Some viruses can infect birds and pigs. If a bird virus, and a human virus meet in a pig and mix some genes, the newly assorted virus can now infect humans. Since it is a newly combined virus, the human immune system has never encountered it before, and cannot fight it straight away. This virus spreads to other people, and an epidemic occurs. Note that no new information has been added, existing information has been re-shuffled to create a combination of information from two different viruses. In other words, this is an example of micro-evolution, using existing information, not evolution in a Darwinian or Neo Darwinian sense. They start and finish as the same kind of virus (i.e. influenza), but with a slightly different compatibility.

Viruses can also change due to mutations (copying errors) in their genes. If the mutation affects the shape of their surface protein (i.e. their “skin”), immune systems and/or antibiotics do not recognise them straight away, and the virus successfully enters and attacks the body, spreading through people, and hence, you got it, an epidemic occurs. This surface protein change can also mean that the virus can attach itself to the cells of other previously non infect-able hosts.

None of these changes are evolution. They simply cause small changes in the already existing proteins, or add different information from other viruses. They do not explain the origin of the proteins or information, and the virus has not changed into another type of virus, it has just been made more compatible. It started out as a virus, and ended up as a virus. It is even given the same name, just with a different number after it (i.e. Influenza A [number or letter]). So, in conclusion, viruses do change, and this may lead to a new epidemic, but no known change in viruses is an example of evolution.

For more on supposedly evolving flu viruses see the question: FLU VACCINES: Do we need new ‘flu shots’ because the influenza virus is evolving? Answer by Diane Eager here.

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