What is life?

“Life is a fascinating thing. We can all recognise it but we cannot define it. It is the most elusive natural property known to science and no definition adequately captures its essence. Moreover, you find the chemicals that make up living things in the composition of inorganic objects also.

Initially, it seems obvious that all life must reproduce itself. However, this allows some inanimate objects to slip into the classification as well. Flames can reproduce, for example, otherwise it would be impossible to light candles. By taking reproduction as a definition, we must consider candles alive also. Using the reproduction property as a characteristic of life excludes some undoubtedly living creatures. For example, mules are born when a male horse mates with a female donkey. This produces a genetically distinct creature, a mule, which happens to be sterile as a species and so incapable of reproduction. By our first definition of life, therefore, we cannot classify a mule as alive. To exclude the flame as a life-form, some definitions specify that only reproducing systems capable of genetic mutation and therefore evolution are alive. However, this definition still does not include the mule.

As a final complication, there are viruses. Unlike a microbe, when a virus is isolated, it is incapable of reproducing. To behave as if it were alive, that is, to reproduce and be capable of Darwinian evolution, it must first invade a microbe and hijack its genetic copying machinery. Scientists still cannot decide whether viruses are to be considered living or not.

In the search for a definition that includes all living things but excludes all non-living things, some scientists are beginning to search beyond traditional biological thinking. According to them, the answer may lie in the mathematics of information theory and the way living things store information in their genes. Yet, it is too early to know if this definition will work any better.”

Não sei de onde retirei este texto, nem quem é o autor, mas trata-se de uma hipótese curiosa, na medida em que remete a procura da resposta para além da Biologia, talvez para “the mathematics of information theory and the way living things store information in their genes”.