Biology loves to categorise and classify and to that end life on our planet neatly falls into 3 distinct groups: Eukaryotes (us and all life we see around us), bacteria and archaea. However, somewhere between these 3 domains of life and everything else on the planet classed as non-living sit viruses. Ask any scientist if a virus is living or non-living and you will likely get a lot of umming and ahhing and nowhere near a simple answer. The wonderful thing about viruses is that they can only be described within a certain context. When floating around in the environment, viruses are completely inert, no different from a piece of dirt or dust. There is nothing to indicate that they are alive; no growth, no energy consumption, and no chemical activity whatsoever. However as soon as a virus reaches a specific living cell it bursts into ‘life’, becoming highly active and taking over the machinery of the cell to multiply itself many times over. The general definition of a virus is as an obligate intracellular parasite, meaning it needs to be inside a cell to function and will, as a result of this, cause damage to its host. Viruses aren’t the sort of people you’d want at a dinner party as they’d eat all the food you cook, all the food in the kitchen and then trash the house just for good measure, before smashing the windows to leave instead of using the door. While viruses have long been thought of as an entity unto themselves who lurk over all 3 domains of life like a heavy rain cloud, this view is starting to shift. In this blog I’d like to discuss a couple of viruses that are completely changing the classical view of viruses and blurring the boundaries between viruses and the other domains of life.
|EM image of mimivirus|
|Darwin's sketch of the tree of life|