In evolutionary biology, the GARD (Graded Autocatalysis Replication Domain) model is a general kinetic model for homeostatic-growth and fission of compositional-assemblies, with specific application towards lipids.
[1] In the context of abiogenesis, the lipid-world[2] suggests assemblies of simple molecules, such as lipids, can store and propagate information, thus undergo evolution.
This is different from the information encoded in RNA or DNA, which is the specific sequence of bases in such molecule.
Thus, the model is viewed as an alternative or an ancestor to the RNA world hypothesis.
β is viewed as a directed, weighted, complex network.
The system is kept away from equilibrium by imposing a fission action once the assembly reaches a maximal size, Nmax, usually in the order of NG.
In 2010, Eors Szathmary and collaborators chose GARD as an archetypal metabolism-first realization.
They introduced into the model a selection coefficient which increases or decreases the growth rate of assemblies depending on how similar or dissimilar they are to a given target.
They found that the ranking of the assemblies is unaffected by the selection pressure and concluded that GARD does not exhibit Darwinian evolution.
Two major drawbacks of the 2010 paper were: (1) the authors focused on a general assembly and not on a composome or compotype (faithfully replicating and quasispecies, respectively); (2) they performed only a single, random simulation to test the selectability.