Why is It Difficult to Define Life?
Perhaps the most compelling reason it is difficult to define life is the lack of objective measuring tools. All of our human methods for defining the undefinable (science, philosophy, religion, metaphysics, etc.) are self-limiting in some way. Unlike other living organisms, human beings seem to be driven to quantify and categorize the world around them. If we can describe a phenomenon such as ‘life’ well enough, we can bring some order out of chaos. The problem is, once one working definition of life has been created, a previously unknown plant or animal may appear and defy the definition. Scientists have several qualifications they use to define life, including the ability to reproduce and a reaction to outside stimuli, such as light or heat. But certain computer viruses can use electronics to replicate themselves, and some inorganic materials can be engineered to respond to outside stimuli- plastics which shrink from exposure to heat, for example. Obviously computer viruses and engin
” draws responses, brief (Joel Achenbach) and in detail (Carol Cleland & Christopher Chyba). What is the minimal complexity required for life? At the end of his Introduction, Moritz summarizes current ideas: “The most elementary [non-parasitic] cells we currently know… have 482 protein-coding genes (most bacteria, such as E. coli, encode for more than 2000 different proteins)” plus some non-protein molecules; of these, “according to the probably best experimental study to date (abstract & full text) the essential ones are 387” and “the likely most accurate hypothetical study (abstract & full text) puts the minimal number of genes at 206. All the proteins produced from these genes are involved in a maze of pathways of metabolism, replication, as well as building and maintenance of structure, which is of bewildering complexity.” Gene-First or Metabolism-First? Scientists currently have two theories about the first functionality in the development toward life; was it genes-first or metabo
