Lionel Sharples Penrose
Annals of Human Genetics, 23, pp. 59-72
1958
Download PDF (1.7Mb) (You need to be registered on forum)The theoretical aspect of self-reproduction seems to have been first seriously considered by von Neuman (1951). Using a theorem, invented by Turing (1937), he was able to infer that the construction of an automatic machine capable of replicating itself was possible. Von Neumann thought that about twelve different kinds of units would be required as building materials but he did not specify how complicated such units would have to be. Moreover, according to Haldane (1954), it was generally believed that a very large total number of units would be needed in the actual machine, perhaps more than 10^5.
The concept of self-reproduction needs to be defined so that any system can be tested to ascertain whether or not it agrees with the rules laid down. A structure may be said to be self-reproducing if it causes the formation of two or more new structures similar to itself in every detail of shape and also the same size, after having been placed in a suitable environment. One of the new structures may be identical with the original one. Alternatively, the original structure may be destroyed in the process of forming two new replicas. Certain conditions are added which exclude all well-known types of physical or chemical chain reactions. First, the replicating structure must be built by assembling simpler units present in the environment. Secondly, more than one design can be built from the same set of units thought the only replicating structure that can be automatically assembled will be one exactly copying a previously existing structure. The pre-existing structure is known as a seed.