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Question #2 Q93 06/02/15 (Tue) 21:00:58 No.126

Hello /science/

Recently, I pondered about the definition of life and the black-and-white thinking associated with it. In school, I learned about the characteristics (ex. reproduction, metabolism, etc.) that need to be there in order to define something as a living system.

Rather than upholding this "it is either alive or not" reasoning, I would like to propose an alternative approach by adding a grey zone. Things can now be sort of alive, based on how many characteristics they have in common with modern cells.

I am interested in your opinions about that point of view.

Professor 06/07/15 (Sun) 14:24:14 No.127

Usually precision is preferable. With a grey zone there might be confusion.

Professor 06/15/15 (Mon) 15:15:55 No.130

Do you have an example of something that's partially alive? I remember reading a while back that fire behaves like a living organism (has metabolism, grows/spreads/reproduces, etc), it's just missing cells/DNA. But fire's just a chemical reaction (though you could argue that organisms are just collections of chemical reactions). The idea of grayscale life is interesting but I can't think of any reason for it, except maybe the whatever directly preceded the first true cells..

Q93 06/15/15 (Mon) 21:07:32 No.133

>>>130

Viruses come to mind. Although they lack metabolic pathways, they can reproduce, evolve and are made of the same molecules (DNA and proteins). As such, I would classify viruses as residents of the grey zone.

The reason why I propose an alternative approach, is to solve the problem of defining what can be considered 'alive' when one looks at the process of abiogenesis and to solve the problem of what we have to detect on other planets when we look for extraterrestrial life forms.

If anyone is interested, I found a paper laying out the approach in much more detail:

Bruylants, G. et al. (2010), "Is it Useful to Have a Clear-cut Definition of Life?

On the Use of Fuzzy Logic in Prebiotic Chemistry", Orig Life Evol Biosph 40, pp. 137–143