A Proposal for an Artificial Life Simulation of Evolving Multicellular Ontogeny

Sharon Minsuk
Dept. of Biology, Indiana University, Bloomington, Indiana, U.S.A.

Abstract:

I propose to create an adaptive computer simulation to explore the evolution of ontogeny, of morphology, and of body plans, in which simple simulated progenitor organisms are subjected to random mutation and to selection based solely on the differential success of different genotype lineages at gathering material and energy resources from their simulated environment, surviving and reproducing. Because development is based on the activity of individual cells, the model will be constructed at the cellular level. On the premise that development and multicellularity evolve hand-in-hand, the correct approach is to model the origin of multicellularity, rather than trying to build a complete multicellular developmental system as a starting point. Self-maintaining, self-replicating unicellular organisms in a complex 2-dimensional environment will be simulated, with emphasis on those features of unicellular organisms likely to be important in multicellularity and development. The genome (executable program code that controls the cell's behavior, and on which the mutation operations are carried out) will be structured to allow complex regulatory interactions between genes (subroutines), and these genes will function in parallel. Furthermore, morphological features at all levels of biological organization evolve because of their usefulness to the organism in interacting with the environment. I propose that these interactions are fundamentally mechanical, and therefore, an important innovation of the simulation will be to model the physics underlying cellular behavior, including the mechanical properties of cells and the role of membranes in mediating environmental interaction, which have not been part of any adaptive simulations yet devised, as well as energetic considerations, which have received more attention. Cells will be modeled at high resolution, allowing for complex membrane shape and interaction with other cells and with the environment, unlike the "billiard-ball" cellular models of previous adaptive simulations. In addition, the simulation will include a high degree of environmental complexity, which has been shown to be important in eliciting the evolution of complex adaptations in adaptive simulations. It is hoped that by focusing the bulk of the effort on laying the proper cellular groundwork, a robust, expandable system can be developed in which multicellularity can arise under selective pressure, as a natural consequence of the capabilities and limitations of cells. This study will bring together the fields of evolutionary developmental biology and artificial life, and address important unresolved questions in both of them.