Self-replication

Exceptions to this pattern are possible. For example, scientists have successfully constructed RNA that copies itself in an "environment" that is a solution of RNA monomers and transcriptase. In this case, the body is the genome, and the specialized copy mechanisms are external.

However, the simplest possible case is that only a genome exists. Without some specification of the self-reproducing steps, a system is probably better characterized as something like a crystal.

Classes of self-replication

• Natural replicators have all or most of their design from nonhuman sources.
• Autotrophic replicators can reproduce themselves "in the wild". They mine their own materials. Usually they are designed by humans, and in particular, can easily accept specifications for human products.
• Self-reproductive systems produce copies of themselves from industrial feedstocks such as metal bar and wire.
• Self-assembling systems assemble copies of themselves from finished, delivered parts.

A self-reproducing computer program

In computer science a self-reproducing computer program is a computer program, that, when executed, outputs its own code. This is also called a quine.
Here is an example program in the Python programming language:

a='a=%s;print a%%`a`';print a%`a`

This approach is common in most self-replicating systems, including biological life, and is simpler in that it does not require the program to contain a complete description of itself.

Applications

A fully novel artificial replicator is a reasonable near-term goal.
A NASA study recently placed the complexity of a clanking replicator at approximately that of a Intel's Pentium 4 CPU. That is, the technology is achievable with a relatively small engineering group in a reasonable commercial time-scale at a reasonable cost.

Given the currently keen interest in biotechnology and the high levels of funding in that field, attempts to exploit the replicative ability of existing cells are timely, and may easily lead to significant insights and advances.

Fields involving study of self-replication

Self-replication in industry

Space exploration and manufacturing

In general, since these systems are autotrophic, they are the most difficult and complex known replicators. They are also thought to be the most hazardous, because they do not require any inputs from human beings in order to reproduce.

A classic theoretical study of replicators in space is the 1980 NASA study of autotrophic clanking replicators, edited by Robert Freitas.

Much of the design study was concerned with a simple, flexible chemical system for processing lunar regolith, and the differences between the ratio of elements needed by the replicator, and the ratios available in regolith. The limiting element was Chlorine, an essential element to process regolith for Aluminum. Chlorine is very rare in lunar regolith, and a substantially faster rate of reproduction could be assured by importing modest amounts.

The reference design specified small computer-controlled electric carts running on rails. Each cart could have a simple hand or a small bull-dozer shovel, forming a basic robot.

Power would be provided by a "canopy" of solar cells supported on pillars. The other machinery could run under the canopy.

A "casting robot" would use a robotic arm with a few sculpting tools to make plaster moldss. Plaster molds are easy to make, and make precise parts with good surface finishes. The robot would then cast most of the parts either from non-conductive molten rock (basalt) or purified metals. An electric oven melted the materials.

A speculative, more complex "chip factory" was specified to produce the computer and electronic systems, but the designers also said that it might prove practical to ship the chips from Earth as if they were "vitamins."

Molecular manufacturing

These systems are substantially simpler than autotrophic systems, because they are provided with purified feedstocks and energy. They do not have to reproduce them. This distinction is at the root of some of the controversy about whether molecular manufacturing is possible or not. Many authorities who find it impossible are clearly citing sources for complex autotrophic self-replicating systems. Many of the authorities who find it possible are clearly citing sources for much simpler self-assembling systems, which have been demonstrated. In the meantime, a LEGO-built autonomous robot able to follow a pre-set track and assemble an exact copy of itself, starting from four externally-provided components, was demonstrated experimentally in 2003.

Merely exploiting the replicative abilities of existing cells is insufficient, because of limitations in the process of protein biosynthesis (also see the listing for RNA).
What is required is the rational design of an entirely novel replicator with a much wider range of synthesis capabilities.

For a discussion of other chemical bases for hypothetical self-replicating systems, see carbon chauvinism.

Industrial assembly

Industrial robots have already been used to assemble robots of the same model, demonstrating self-assembling systems.

See also

References