What is Life?

For a change I think I will start this blog by talking about one of my other courses rather than the phage hunt course I am supposed to talk about. Instead I will discuss astronomy. One of the most interesting parts of astronomy is speculating about the possibility of finding extra-terrestrial life. Of course there would be many challenges first the sheer scale of the universe, along with the background radiation that means we can only search for signals at few frequencies, the fact that life could be microscopic and even that life might not be too happy about being found… However one thing that science fiction seldom includes but which was brought up by Dr Ian Bond is that even if we did find life we might not even realise it because it would be so “alien”.

So I started to think about what extra-terrestrial life might be like if it could be so different to life on earth that we don’t recognise it. Then it occurred to me that we already right here on earth have things that we cant be completely sure of their status as life. This brings me to the course I was supposed to talk about. Viruses are in essence a bundle of genetic material (DNA or RNA) surrounded by a protein coat. They therefore have the same material that allows us to live and they certainly reproduce and evolve by natural selection but does that make them alive?

It does not help that we don’t think much about what makes something alive we usually know life when we see it but if we cant easily define it in an objective way. There have been attempts to define it but these are not necessarily ideal definitions. I learned in year 11 of the acronym MRS GREN that includes the 7 signs of life movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. This seemed very easy at the time so a bee is alive but a river is not alive and fire is almost alive but it is not sensitive. Using this definition a virus is not alive as it does not excrete and cannot move independently.

Later though I found out that it used to be MRS C GREN the C being circulation. The C was removed after it was recognised that bacteria are do not have circulatory systems. This problem here was that the definition was changed to suit what we already consider to be life rather than being used to discern what is or isn’t life. Why then couldn’t you drop other letters and say that a virus is alive. Admittedly life is not the only concept that is difficult to define (science, culture, consciousness…) but these are not the focus of this blog as I don’t want to spend my whole summer holidays writing it even if I was allowed to.

However it seems important to know what life could be. Even if it is not useful to know if a virus is alive maybe so we could know if we find alien life or whether scientists could really produce artificial life. So does the fact that virus can reproduce and evolve by natural selection make it alive? It may well not fire can make copies of itself and natural selection in fact works on anything that can make non identical copies of itself. The historian/scientist Jared Diamond has hypothesised that societies can evolve in a similar way and evolution is fairly easily repeated on a computer. The fact that viruses contain genetic material is also not relevant as any organism when killed still contains genetic material.

It has been hypothesised that viruses may have evolved from cells that when parasitising other cells became progressively simpler which would seem to suggest that they must be alive. However unless one subscribes to the idea of creationism you would have to consider that life itself must have arisen from non living things so the reverse happening does not seem implausible (in any case this is merely a hypothesis). What seems even more convincing (at least to me) though is that some viruses can in fact infect other viruses which makes it impossible to say that they simply something that infects life but is not itself alive.  The most logical solution is probably that there is no sharp divide between life and non living things. That is that there is a set of characteristics we group together and call life but which can exist in varying combinations and we can choose any of them as being essential or unnecessary.  Viruses have been described in one article as biological replicators noting the important thing about viruses is that they interact with life. (The article also notes that everything that we have observed natural selection affecting has some biological origin such as a computer program that is man made). So in nature there entities that replicate, move react to their environment and many other things and entities that don’t it is up to each individual to decide whether those things are alive.


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