complexity and parasites

 Our new paper published today, open access:

Simon Hickinbotham, Susan Stepney, Paulien Hogeweg.
Nothing in evolution makes sense except in the light of parasitism: evolution of complex replication strategies.
Royal Society Open Science, 8(8):210441, 2021.

Abstract: Parasitism emerges readily in models and laboratory experiments of RNA world and would lead to extinction unless prevented by compartmentalization or spatial patterning. Modelling replication as an active computational process opens up many degrees of freedom that are exploited to meet environmental challenges, and to modify the evolutionary process itself. Here, we use automata chemistry models and spatial RNA-world models to study the emergence of parasitism and the complexity that evolves in response. The system is initialized with a hand-designed replicator that copies other replicators with a small chance of point mutation. Almost immediately, short parasites arise; these are copied more quickly, and so have an evolutionary advantage. The replicators also become shorter, and so are replicated faster; they evolve a mechanism to slow down replication, which reduces the difference of replication rate of replicators and parasites. They also evolve explicit mechanisms to discriminate copies of self from parasites; these mechanisms become increasingly complex. New parasite species continually arise from mutated replicators, rather than from evolving parasite lineages. Evolution itself evolves, e.g. by effectively increasing point mutation rates, and by generating novel emergent mutational operators. Thus, parasitism drives the evolution of complex replicators and complex ecosystems.

Parasites drive complexity.  But how?  Here, we examine the outcomes of some computer experiments using our Stringmol automata chemistry (where ‘molecules’ are short assembly language programs, that bind and execute to copy each other), where we can see parasites evolve, then see the measures that evolve that replicators use to guard against parasites, then the counter-measures that parasites use to get round these, then the counter-counter-measures, and so on.

evolution of complex execution strategies (see paper for details)

Interestingly, we don’t see separate lineages of replicators and parasites co-evolving, but rather each new strain of parasite evolves from a replicator, so that it can exploit that replicator’s defence code itself.

The original bioRxiv version of the paper got a mention in preLights.