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GENERAL BEHAVIOR OF THE SYSTEM

Once the soup is full of replicating creatures, individuals are initially short lived, generally reproducing only once before dying, thus individuals turn over very rapidly. More slowly, there appear new genotypes of size 80, and then new size classes. There are changes in the genetic composition of each size class, as new mutants appear, some of which increase significantly in frequency, eventually replacing the original genotype. The size classes which dominate the community also change through time, as new size classes appear, some of which competitively exclude sizes present earlier. Once the community becomes diverse, there is a greater variance in the longevity and fecundity of individuals.

In addition to an increase in the raw diversity of genotypes and genome sizes, there is an increase in the ecological diversity. Obligate commensal parasites evolve, which are not capable of self-replication in isolated culture, but which can replicate when cultured with normal (self-replicating) creatures. These parasites execute some parts of the code of their hosts, but cause them no direct harm, except as competitors. Some potential hosts have evolved immunity to the parasites, and some parasites have evolved to circumvent this immunity.

In addition, facultative hyper-parasites have evolved, which can self-replicate in isolated culture, but when subjected to parasitism, subvert the parasites energy metabolism to augment their own reproduction. Hyper-parasites drive parasites to extinction, resulting in complete domination of the communities. The relatively high degrees of genetic relatedness within the hyper-parasite dominated communities leads to the evolution of sociality in the sense of creatures that can only replicate when they occur in aggregations. These social aggregations are then invaded by hyper-hyper-parasite cheaters.

Mutations and the ensuing replication errors lead to an increasing diversity of sizes and genotypes of self-replicating creatures in the soup. Within the first 100 million instructions of elapsed time, the soup evolves to a state in which about a dozen more-or-less persistent size classes coexist. The relative abundances and specific list of the size classes varies over time. Each size class consists of a number of distinct genotypes which also vary over time.

The rate of evolution increases with the mutation rate until the system becomes unstable, and the community dies at rates above one mutation per four generations. Ecological interactions are richer and more sustained at slightly lower rates, one mutation per eight or 16 generations. At mutation rates of one per four generations, under selection for small sizes, creatures will optimize to a genome size in the 22 to 30 instruction size range within as little as 300 million instructions of elapsed time. Each of these runs will reach a local optima which it evidently cannot escape from, although it may not be the global optima.



next up previous
Next: INCREASING COMPLEXITY Up: SUMMARY Previous: SUMMARY



Thomas S.Ray
Thu Aug 3 15:47:29 JST 1995