Langton's loops

Langton loops (English Langton's loops) are a special form of artificial life; they were designed in 1984 by the theoretical biologist Christopher Langton, one of the founders of the research discipline of Artificial Life.

The " organism" which is capable of self-replication, which can be simulated in a cellular automaton, consist of an annular array of cells which contain the " genetic information ". These cells are surrounded by a protective shell in which they rotate constantly. At a certain point the cell strand breaks with the " genes " on the envelope, and the organism forms one arm ( almost a pseudopod ), whereas in the entering a full copy of the gene sequence. This causes to grow the arm to a new ring to close ( the daughter ring) and eventually peel off from the parent ring. Then the two genetically identical organisms are willing to but repeated replication.

History

1947, John von Neumann Universal Constructor with the first time a universal cellular automata with the ability to replicate itself before which any pattern including its could reproduce itself. This machine was due to its universality necessarily very complex, in 1968 was Edgar F. Codd, the number of cell states at least reduce from 29 to 8. Christopher Langton finally succeeded in his design, in turn, a considerable simplification by deliberately on the - renounced universality and was limited to the ability to replicate itself - in biological systems anyway not given. His loops are based on one of the simplest elements in Codd's automata, the so-called Periodic emitter (periodic pulser on von Neumann ) - which is responsible for replication essentially organ.

Description

Designed by Langton Cellular automaton is two-dimensional with von Neumann neighborhood and 8 cell states. The initial configuration consists of 86 cells ( counts only those with a different from 0 initial state, see picture). There are hundreds of rules that specify the state changes of each cell in the transition from one to the next generation.

Initial structure

The sheath is formed of cells having State 2, to surround the annular cell string of the branching arms of the state of the first cells, the genome is encoded as a sequence of instructions on the ring. An instruction in each case consists of a cell in one of the states 4, 5, 6 or 7, followed by a cell from the state 0 This gene sequence rotates in a counterclockwise direction in the annular envelope.

Replication and development

Where a one instruction at the junction of the arm, so it is replicated: the original continues to circulate through the ring, the copy enters the arm. ( In the example on the right, the instruction has 07 reached the junction and would be replicated next. ) At the end of the arm, the protein encoded by the gene sequence of instructions to control the protuberance of the pseudopodium, growth and bending of the arm, the design of the daughter loop and the separation of the parent loop. Thus arise through a similar process of budding new organisms with an identical genome.

In analogy to gene expression Langton compared the replication at the junction of the arm with the transcription, the implementation of the instructions at the end of the arm with the translation.

Colony formation

A pseudopod can not penetrate into the occupied space of an existing loop. This has the consequence that organisms which are surrounded on several sides by other organisms, can not further replicate; they die and form with the neighboring dead organisms - similar to a coral colony - a colony of a skeleton inactive loops with a thin shell continued reproducing, living organisms.

Unless is unlimited habitat available, the size of such a colony is limited, it asymptotically approaches the value, the size of the living space into cells indicates.