MadSci Network: Biochemistry

Re: Is there any reason why life couldn't not need water?

Date: Fri Jul 30 02:47:30 1999
Posted By: Ewen McLaughlin, Lecturer, Chemistry, Swansea College
Area of science: Biochemistry
ID: 932678740.Bc

To rephrase your question: does life need water?
In theory, life does not need water.
In fact, if you are willing to extend your definition of 'life' then there 
is already at least one example: ideas and information has life in the 
sense that it is reproduced and evolves. This is Richard Dawkins' 'meme' 
idea, from The Selfish Gene.
It may become possible to create machines that can reproduce (a robot that 
can build a copy of itself, for example). Would these be living?
But that's not quite the question, is it? I guess you want to know about 
chemical-based life such as we have here on Earth - such as we are. Well, 
if you restrict the definition of life to very similar chemistries to our 
own, then water is essential. Proteins, DNA, lipids and carbohydrates 
would have radically different properties in a solvent other than water 
(liquid ammonia, say). So if you want life-as-we-know-it then you need 
water. It has been said that we are water-based life, which might be 
informative to any extraterrestrials who want to know, but is so obvious 
to any biologist that it's rarely considered important.
Could life be based on (say) liquid ammonia as a solvent? We don't know 
for sure as chemistry in non-water solvents is not nearly as well studied 
as water-based chemistry. I'm pretty certain that it is possible to have 
some sort of life in non-water solvents, however; chemistry is too 
diverse, in my opinion, to be able to make life in only one solvent.
Until we find life on another planet, though, this is all just 
speculation. Nobody has really reproduced water-based life from chemicals 
so the chances of discovering non-water based life when we don't even know 
what such life would be like are remote.
Ewen McLaughlin

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