Science defines most things in the world, but do you know that science has no proper definition for life?
World religion including Hinduism, Christianity or Islam adheres to the ‘meaning’ of life more than the definition of life. Many early western philosophers used the similar notion ‘soul’ or vitality elements to define life. However, as much as we see life flourishing in abundance, modern day scientists are still finding the proper definition of life as a staggering act. The spiritual aspects regarding life remained despite the scientific approaches supporting the origin of life (e.g Haldane, Oparin, Urey and Miller etc).
I will present some of the definitions of life and their contradictions in this post. Firstly, its important to know that the definition itself can be broken down in many ways in terms of physiological, metabolic, biochemical, genetic and thermodynamic forms (C.E Cleland, 2002). All of them had/have strong counter arguments.
For example, NASA’s working definition is: “Life is a self sustained chemical system capable of undergoing Darwinian evolution” (Joyce, 1994ab). Despite being ‘considerably’ accepted within the astrobiological community, Darwinian evolution requires the ability to reproduce. Consequently, a conclusion can be drawn that worker ants or mules should be considered as non-life although we know otherwise intuitively.
A second example, Guimaraes defines “The functions, which are called life are metabolism, growth, and reproduction with stability through generations” (Kolb, 2006). If we look at ‘growth’ as a criteria, the same is also validated for inorganic crystals, which could grow with the right nutrients. Development in organism get adjusted to regulated trajectory, the similar happens when local surface trajectory influence the course of metal oxides crystals (Cairns-Smith, 1982). Even clouds ‘grow’ and become numerous, depending on the weather patterns.
In terms of thermodynamics, life have a low entropy system. This means life maintains a high degree of order. On close examination, life is very selective, for example; only left handed amino acid (protein builders) and right handed sugar (DNA) are utilized to perform life’s activities. This is referred to as homochirality. Even the simplest bacteria Mycoplasma pneumonia when studied in detailed is highly complex. However, a chemical system criteria alone is not enough since many non-living entities do those as well (i.e formation of stars).
Don’t you think it’s rather awkward that we only know life intuitively (on earth at least) but can’t properly define it. The importance of defining life would be very useful since we can streamline all our technical approaches to promisingly identify alien life forms in space (Titan, Europa), unless the green man himself decides to land on earth and say ‘こんにちわ’ (hello in Japanese), millions of dollars could be saved.
On the contrary, the unpopular term “autopoiesis” to define life is slowly making a comeback, despite several misconception and misgauge of the term within science (Boden, 2000). The word ‘autopoiesis’ was first coined by the Chilean duo Humberto Maturana and Francisco Varela in the early 1970′s. (By the way Francisco is the father of Leonor Varela).
Their definition of life was ill received from mainstream scientist because it was not in tandem with Darwin’s theory of evolution and also DNA making its entry as an important aspect in biology during that time.
Autopoiesis literally means self-producing in Greek. The authors described that life is defined as a unity with a network of producing component (Maturana et. al 1974), in other words an autopoiesis system is capable of organizing the production of its own components that is within a boundary (a membrane is a boundary of a cell) (Luisi, 2003) The term deliberately down plays the importance of genetics (DNA and/or RNA) and focuses on the boundary which holds life’s system. This is simply because Darwinian theory reflects more on the general populations than on the individuals. Before his death in 2001, Varela expressed autopoesis in the following ways: verifying (1) whether the life’s system has a semipermeable boundary that (i.e cell membrane) (2) life is produced from within the system (i.e metabolism) and (3) that encompasses reactions that re-generate the components of the system (i.e transcription) (Varela 2000). Autopoiesis is gaining popularity and few are already using it for synthetic biology (i.e Luisi’s group) and the origin of life field specifically to recreate the proto-cell (Morowitz‘, Deamer‘, Szostak‘ groups).
As mentioned earlier, the specific definition of life is important if we are to understand our origins and to find aliens (i am being real here). But, with the latter, we can’t really rely on earth’s life definition (even if have one) itself since there is a possibility that aliens may be define in other ways beyond our current state of biology.
Ps: I would advice readers who don’t have a formal biology/chemistry background to click on the hyperlinks if they find it difficult digesting the post. I have included wikipedia pages, youtube links and journals (you can download some of it). So do take your time understanding it. Also do give some thoughts on what you think the definition of death might be.
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