Viruses in Life

Are viruses life? Probably not - even though they have genetic code and protein they can't reproduce without invading a living cell. But they can have an immense impact on how life evolves.

Most of the time when we hear about a virus in the news, its something bad. Viruses cause all sorts of diseases, everything from the flu to HIV. However, viruses might actually have been the most important factor in the evolution of complex life. Here's how:

Most of the time when people think about evolution they think about mutations. A mutations is basically a random error in the reproduction of an organism's genetic code. Sometimes these random errors are bad, most of the time they don't do much of anything, and every once in a while they can actually be good for the organism in whatever environment its in. But mutations alone are not adequate to explain for complexity. Instead something called lateral gene transfer is necessary.

Lateral gene transfer is the transfer of genetic code from one organism to another such that the new code becomes a part of the DNA or RNA of the organism. Lateral gene transfer is in like the internet of evolution. Information is available, and an organism can make the available genetic code part of its own code, just like you can find pretty much anything you need on the internet (or course, microbes can't search for what they want, but I'm tryin' here). Mutation is more like trial and error by an individual trying to figure something out. Think 13th century alchemist trying to come up with a new material by experimenting day after day. Both are useful, but lateral gene transfer was probably much more productive in evolving life early on. This can be done in a few ways, including contact between cells, incorporation from the environment, and also by viral infection.

So, how important is this anyways? Consider a few facts. First, viruses are the most abundant 'biological' entity on the Earth. Also, lateral gene transfer may be the most important mechanism for acquiring new genes. Finally, viruses are known to have useful genetic code; some marine phages (viruses that attack marine bacteria) contain the code necessary for photosynthesis. These facts put together imply that viruses may have been responsible for spreading many genetic innovations in early life. One scenario could be that one organism developed the ability to use photosynthesis for light. Somehow, a virus gets that genetic code necessary for photosynthesis. The virus multiplies, 'infecting' other organisms with the photosynthesis genes. Soon, photosynthesis becomes ubiquitous, or common, throughout the environment.

Viruses are important. While they might seem bad at present day, in the long-term evolution of life on this planet, viruses may have been essential through lateral gene transfer. In fact, without viruses, it is unlikely that complex organisms like human beings could exist.

Sources: Planets and Life, Sullivan & Baross