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Saturday, June 24, 2017

Cellular Automata Laboratory: Reproduction, Evolution, Abiogenesis, and Sex

The latest collection of rules for Cellular Automata Laboratory (CelLab) illustrates aspects of self-reproduction and analogues to biological systems. Basic self-reproduction is demonstrated by the Langton rule, in which a loop of digital “DNA” provides the instructions to replicate itself and its enclosing structure, creating new identical digital organisms.

Ever since John von Neumann discovered the first self-reproducing cellular automaton rule in 1952, a challenge has been to find simpler and faster-replicating rules. Von Neumann's original rule used 29 states, while Langton, in 1984, simplified this to just 8 states, an initial pattern of 86 cells, and 151 generations to replicate. The latest update to CelLab includes the Byl and Chou-Reggia rules, which further simplify a replicator to (Byl) 12 cells, 6 states, and 25 generations to replicate; and (Chou-Reggia) 5 cells, 8 states, and replication in just 15 generations.

These are all exact replication: every descendant is a precise copy of its ancestor. Biological replication is messier yet more powerful, since it permits evolutionary change and adaptation to the environment. In 1998, Hirokia Sayama published Evoloops, a generalisation of Langton's replicator which allows individual replicators that collide in a world of limited space to mutate, often leading to selection for smaller, faster-replicating organisms not present in the original simulation. Precisely the same phenomenon is observed in bacteria grown with limited resources. Evoloops can also demonstrate abiogenesis: the appearance of replicators from random interactions of non-replicating structures in a “primordial soup”.

In 2007 and 2009, Nicholas Oros further generalised Evoloops to create Sexyloop, which stirs recombination of genetic information, similar to that which occurs in sexual reproduction, into the mix. Now, when digital organisms interact, they can exchange genetic information, so a behaviour which appears spontaneously in one organism can propagate to others, similar to gene transmission in bacterial conjugation and, if adaptive, come to dominate the population.

Run the Byl replicator in CelLab
Run the Chou-Reggia replicator
Run Evoloops evolution experiment
Run Evoloops abiogenesis experiment
Run Sexyloop simulation

Posted at June 24, 2017 23:27