Evolution of differentiated multi-threaded digital organisms

Presents a descriptive natural history of the results of the evolution of differentiated multi-threaded (multi-cellular) self-replicating machine code programs (digital organisms), living in a network of computers, called the Tierra network. Programs are differentiated in that different threads execute different code (i.e. they express different genes). The seed organism develops into a mature ten-celled form, differentiated into a two-celled reproductive tissue and an eight-celled sensory tissue. The sensory threads obtain data about conditions on the machines in the network, and then process that data to choose the best machine to migrate to or to send the daughter to. Evolution leads to a diversity of algorithms for foraging for resources, primarily CPU time, on the network.