Hand coded bots generally "devolve" in an evo-sim, meaning the hand-authorred code stops functioning over time. This is because all that hand-authorred DNA was written without context - it didn't evolve in conjuction with an ecosystem or under environmental or preditor or compitition induced selection pressures and thus when the bot is released into an evo-sim and subjected to mutations and selection, there is little or no selection pressure to preserve the DNA as written. Selection is in operation to be sure and the bot is evolving, but selection is selecting for things that tend to break the fragile, hand-authored DNA - things like faster replication. The DNA has to come down off that impossible peak in the fitness landscape before it can start it's slow journey back up the mountain. Bascially, a hand-authorred bot is a super specialized, unrealistic aberation of nature, a boy in a bubble ill suited to survive in the "real world".
Zerobots or very very simple hand-authorred bots are a better starting poihnt for evo sims in that they don't have to fall off their peak first. There, you generally see increases in functionality and complexity over time though I will be the first to admit we are still toying with excactly what is necessary w.r.t. selection pressures to provoke richer adaptions such as conditonal logic.
