When the simulator is run over long periods of time, hundreds of millions or billions of instructions, various patterns emerge. Under selection for small sizes there is a proliferation of small parasites and a rather interesting ecology (see below). Selection for large creatures has usually lead to continuous incrementally increasing sizes (but not to a trivial concatenation of creatures end-to-end) until a plateau in the upper hundreds is reached. In one run, selection for large size lead to apparently open ended size increase, evolving genomes larger than 23,000 instructions in length. These evolutionary patterns might be described as phyletic gradualism.
The most thoroughly studied case for long runs is where selection, as determined by the slicer function, is size neutral. The longest runs to date (as much as 2.86 billion Tierran instructions) have been in a size neutral environment, with a search limit of 10,000, which would allow large creatures to evolve if there were some algorithmic advantage to be gained from larger size. These long runs illustrate a pattern which could be described as periods of stasis punctuated by periods of rapid evolutionary change, which appears to parallel the pattern of punctuated equilibrium described by [15,19].
Initially these communities are dominated by creatures with genome sizes in the eighties. This represents a period of relative stasis, which has lasted from 178 million to 1.44 billion instructions in the several long runs conducted to date. The systems then very abruptly (in a span of 1 or 2 million instructions) evolve into communities dominated by sizes ranging from about 400 to about 800. These communities have not yet been seen to evolve into communities dominated by either smaller or substantially larger size ranges.
The communities of creatures in the 400 to 800 size range also show a long-term pattern of punctuated equilibrium. These communities regularly come to be dominated by one or two size classes, and remain in that condition for long periods of time. However, they inevitably break out of that stasis and enter a period where no size class dominates. These periods of rapid evolutionary change may be very chaotic. Close observations indicate that at least at some of these times, no genotypes breed true. Many self-replicating genotypes will coexist in the soup at these times, but at the most chaotic times, none will produce offspring which are even their same size. Eventually the system will settle down to another period of stasis dominated by one or a few size classes which breed true.