January – 2004

The ``RNA World'' is possibly today's most popular theory for the origins of life cite{Gilbert1986,Joyce2002}. Because RNA molecules can act as catalysts in addition to acting as templates, it is hypothesized they might have been able to do both: to store alphabet-based genetic information emph{and} to catalyze their own creation. Life, according to this theory, began when certain RNA molecules achieved the capability to replicate themselves. This scenario, despite its elegance, suffers from difficulties.

In an attempt to come up with a probable scenario, having observed that no known bio-molecule is capable of self replication in its naked form, it has been suggested that self replication might not have been achieved by a single molecule, but rather by a molecular ensemble cite{Kauffman1993}. This work is based on ``The Lipid World'' scenario cite{Segre2001a} which follows that line of thought. The scenario assumes that self-replication was initially achieved by non-covalent assemblies of lipid-like molecules that contained mutually catalytic sets cite{Segre2000a}. Such self-replication is remarkably easier to achieve. RNA according to this scenario, while possibly playing an important role, came later.

Lipidia is a new simulation system that is related to the ``Lipid World'' scenario. Lipidia allows for conducting experiments with a population of assemblies containing lipid-like molecules on a two dimensional grid. The dynamics of the assemblies is modelled using the Graded Autocatalysis Replication Domain (GARD) model. New experiments using a finite environment model with GARD were conducted with Lipidia. The experiments show that more self-replicating assembly species appear when using a model of finite environment than when using a model of infinite environment. In many species the number of individuals increases as well.

No background knowledge is required.