Evolution of differentiated expression patterns in digital organisms
  We investigate the evolutionary processes behind the development and optimization of multiple threads of execution in digital organisms using the avida platform, a software package that implements Darwinian evolution on populations of self-replicating computer programs. The system is seeded with a linearly executed ancestor capable only of reproducing its own genome, whereas its underlying language has the capacity for multiple threads of execution (i.e., simultaneous expression of sections of the genome.) We witness the evolution to multi-threaded organisms and track the development of distinct expression patterns. Additionally, we examine both the evolvability of multi-threaded organisms and the level of thread differentiation as a function of environmental complexity, and find that differentiation is more pronounced in complex environments. 
Charles Ofria, Christoph Adami, Travis C. Collier, and Grace K. Hsu   (California Institute of Technology)