Is it easy to draw the line between non-living chemistry and life?
Are there, for example, chemical chains that grow to a certain size and then divide, leaving each "child" chemical to grow and divide again?
If not, what is absolute minimum of complexity for growth and reproduction behaviour?

Is there anything that is self-replicating without DNA?
Is such a thing feasible with a little imagination?

Sorry if this question is too much in the realm of biochemistry

Put simply, there is no easy line between life and non-life. For instance, there is a fair amount of disagreement among biologists on whether viruses are living or not. If you define life as having the ability to reproduce, then viruses can be "alive" because they do just that. However, viruses are so specialised that they generally rely on the intracellular mechanisms of a host organism to reproduce and cannot reproduce on its own. Thus viruses can be dormant and in that sense, essentially "non-living", for extended periods of time in the absence of host organisms. They also share the same inheritable chemical substances, i.e. DNA and/or RNA, with other living organisms and presumably share a common ancestry - but whether viruses are primitive or highly derived is not fully understood.

On the other hand, clay minerals are known to catalyse organic chemical reactions. The use of clay minerals as a catalyst seems to be an active area of research in industrial sciences. It has been hypothesised that early organics (including nucleic acids) may have been catalysed by clay minerals to "self-replicate" in the absence of or before the emergence of cells.

Last edited by Manabu Sakamoto (16th Mar 2008 23:13:23)

And don't fopget prions! These are even more simple than viruses (BSE is a famous example), they are basically malformed proteins that can cause other proteins to malform like themselves. So they kind of replicate....ish. I do not think anoyone would consider them alive, but they are an organic chemical that can replicate (providied there are others around for it to act on, rather like a virus).