Can replicators that copy whatever they bind survive in a soup where most molecules never copy anything? Blue circles are replicators, green circles are catalysts and amber circles are substrates. Each copy appears next to the molecule it was copied from.
Try this Set mutation-rate to 0; it takes effect live. Copies are now always faithful, and replicators are slowly diluted by the catalysts and substrates they copy. In most runs they die out within about 2,500 ticks and the rest of the soup follows; in the others the substrates die out first and replicators and catalysts carry on alone.
About this model Where it ends up
Stringmol is an artificial chemistry built by Simon Hickinbotham, Susan Stepney and colleagues at the University of York around 2010. Its molecules are strings of symbols that bind with a probability set by how well their sequences align, then run as small programs. A replicase copies whatever molecule binds to it, so copying errors produce parasites that are copied but copy nothing. This model keeps the copy-what-you-bind rule and replaces the strings with three fixed kinds of molecule.
Molecules wander a 33 × 33 grid that wraps at the edges, turning by up to 30° and moving 0.7 of a patch each tick. In random order, each molecule binds one random molecule within 3 patches. A replicator with at least 30 energy, on a patch with more than 2 feedstock, copies that partner whatever its kind: it pays 14 energy and 1.5 feedstock, and the copy appears next to its template with 14 energy and, with chance mutation-rate %, a random kind. Then, if the partner is a catalyst and the patch has more than 1 feedstock, the molecule gains 4 energy for 0.5 feedstock. Every molecule loses 0.25 energy a tick and breaks down when its energy runs out, or at random with probability 1/mean-lifetime per tick, returning 1 feedstock to its patch. Feedstock regrows by feedstock-rate a tick, up to 3 per patch.
There are no strings, no binding by sequence and no programs: kind is a fixed label, and the symbols sym1 to sym3 are copied and mutated but affect nothing. A copy is made in one step, not symbol by symbol. Decay is a fixed chance per tick, as in Stringmol, but catalysts as the only source of energy are this model's addition. Because of them, replicators with energy to spare usually sit next to catalysts, and about half of all copies are catalysts. Replicators settle at about a quarter of the soup. About one new replicator in five is a garbled copy of a catalyst or substrate, and that trickle keeps them from being diluted away: with mutation-rate at 0 they die out in most runs.
Idea Simon Hickinbotham · Susan Stepney
MathPets MathPets · org
