  Researching the conditions for the emergence of life -- not necessarily as it
is, but as it could be -- is one of the main goals of Artificial Life.
Artificial Chemistries are one of the most important tools in this endeavour,
as they allow us to investigate the process by which metabolisms capable of
self-reproduction and -- ultimately -- of evolving, might have emerged. While
previous work has shown promising results in this direction, it is still
unclear which are the fundamental properties of a chemical system that enable
emergent structures to arise. To this end, here we present an Artificial
Chemistry based on Combinatory Logic, a Turing-complete rewriting system, which
relies on a minimal set of possible reactions. Our experiments show that a
single run of this chemistry starting from a tabula rasa state discovers with
no external intervention a wide range of emergent structures, including
autopoietic structures that maintain their organisation unchanged, others that
grow recursively, and most notably, patterns that reproduce themselves,
duplicating their number on each cycle. All of these structures take the form
of recursive algorithms that acquire basic constituents from the environment
and decompose them in a process that is remarkably similar to biological
metabolisms.
