Graded Artificial Chemistry in Restricted Boundaries

The question of the origin of life is addressed by artificial life research, particularly in the realm of artificial chemistry. Such artificial chemistry is described by our Graded Autocatalysis Replication Domain (GARD) model. GARD depicts an unorthodox scenario suggested for emergence of life – the 'lipid world'. The model concerns molecular assemblies with mutual catalysis in an environment containing a plethora of molecular species. Many aspects of GARD were amply discussed. Here we concentrate on the importance of size constraints as depicted by the basic model and several of its variants. Occasional fission of a GARD assembly, which restricts the assembly size, is crucial for generating compositional quasistationary states ('composomes'). In a spatial version of GARD, bounded environments yield spontaneous emergence of different ecologies. Limiting the size of a population of GARD assemblies gives rise to a complex population dynamics. The last example, with possible wider impact to chemistry and nano-technology, suggests that size limit can give rise to spontaneous symmetry breaking. This latter result is compared to the classic Frank's model for homo-chirality, which requires explicit inhibition. We conclude that size restrictions are fundamental in the field of origin of life and artificial life, not only in order to facilitate evolutionary processes, as previously suggested, but also, for augmenting the dynamics portrayed by different scenarios and models.