Size selection and adaptive evolution in an artificial chemistry.

A simple artificial chemistry for the Squirm3 artificial environment, consisting of replicators that produce quasi-universal enzymes, is presented. The aim of this system is twofold: first, to demonstrate the survival of extracellular replicators despite the presence of faster-replicating parasites; second, to observe the evolution of adaptively useful enzymes. Accomplishing these goals will underpin future attempts to attain open-ended and/or creative evolution in the Squirm3 environment. The first aim is achieved by attaching enzymes to their replicators. Our software implementation demonstrates replicators with 10 bases prospering in the presence of parasites with zero bases. To accomplish the second aim, a process for creating selection pressure toward longer molecules is introduced. The evolution and subsequent dominance of a replicator that produces an adaptively useful enzyme is demonstrated experimentally. Finally, we comment on the crucial role played by neutral evolution and discuss the biological significance of our results.