Self-replication 29549 223797270 2008-07-05T21:22:10Z SteveBaker 252076 Reverted edits by [[Special:Contributions/71.114.6.184|71.114.6.184]] ([[User talk:71.114.6.184|talk]]) to last version by XLinkBot {{seealso|Biological reproduction}} '''Self-replication''' is any process by which a thing might make a copy of itself. [[Cell (biology)|Biological cell]]s, given suitable environments, reproduce by [[cell division]]. During cell division, [[DNA]] is replicated and can be transmitted to offspring during [[reproduction]]. [[virus (biology)|Biological viruses]] can reproduce, but only by commandeering the reproductive machinery of cells through a process of infection. [[Computer virus]]es reproduce using the hardware and software already present on computers. [[Meme]]s reproduce using the human mind and culture as their reproductive machinery. ==Overview== ===Theory=== {{Unreferencedsection|date=September 2007}} Early research by [[John von Neumann]] established that one common form of a [[replicator]] has several parts: *A [[genome]], a compact, usually error-resistant representation of the replicator's stored algorithm.{{Fact|date=September 2007}} Biologically, this is [[DNA]]. *A specialized set of mechanisms to copy and repair the genome, using resources gathered by the body. Biologically, this is something like [[DNA polymerase]]. *A body, which gathers resources and energy, and interprets a stored [[algorithm]]. Biologically, these are [[ribosome]]s. 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 genome-only system is probably better characterized as something like a [[crystal]]. ===Classes of self-replication=== Recent research [http://www.MolecularAssembler.com/KSRM/5.1.htm] has begun to categorize replicators, often based on the amount of support they require. *Natural replicators have all or most of their design from nonhuman sources. Such systems include natural life forms. *[[Autotroph]]ic replicators can reproduce themselves "in the wild". They mine their own materials. It is conjectured that non-biological autotrophic replicators could be designed by humans, and could easily accept specifications for human products. *Self-reproductive systems are conjectured systems which would produce copies of themselves from industrial feedstocks such as metal bar and wire. *Self-assembling systems assemble copies of themselves from finished, delivered parts. Simple examples of such systems have been demonstrated at the macro scale. The design space for machine replicators is very broad. A comprehensive study[http://www.MolecularAssembler.com/KSRM/5.1.9.htm] to date by [[Robert Freitas]] and [[Ralph Merkle]] has identified 137 design dimensions grouped into a dozen separate categories, including: (1) Replication Control, (2) Replication Information, (3) Replication Substrate, (4) Replicator Structure, (5) Passive Parts, (6) Active Subunits, (7) Replicator Energetics, (8) Replicator Kinematics, (9) Replication Process, (10) Replicator Performance, (11) Product Structure, and (12) Evolvability. ===A self-reproducing computer program=== {{main|Quine (computing)}} 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 (computing)|quine]]. Here is an example program in the [[Python (programming language)|Python programming language]]: :<code>a='a=%s;print a%%`a`';print a%`a`</code> A more trivial approach is to write a program that will make a copy of any stream of data that it is directed to, and then direct it at itself. In this case the program is treated as both executable code, and as data to be manipulated. 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. In many programming languages an empty program is still a legal program, which executes without producing errors or any other output. The output is thus the same as the source code, so the program is trivially self-reproducing. === Self-replicating tiling === [[Image:Self-replication of sphynx hexidiamonds.svg|frame|Four 'sphinx' hexiamonds can be put together to form another sphinx.]] In [[geometry]] a self-replicating tiling is a tiling pattern in which several [[congruent]] tiles may be joined together to form a larger tile that is similar to the original. This is an aspect of the field of study known as [[tessellation]]. The "sphinx" [[hexiamond]] is the only known self-replicating [[pentagon]].<ref>For an image that does not show how this replicates, see: Eric W. Weisstein. "Sphinx." From MathWorld--A Wolfram Web Resource. [http://mathworld.wolfram.com/Sphinx.html http://mathworld.wolfram.com/Sphinx.html]</ref> For example, four such [[concave_polygon|concave]] pentagons can be joined together to make one with twice the dimensions.<ref>For further illustrations, see [http://www.geoaustralia.com/italian/Sphinx/Guide.html Teaching TILINGS / TESSELLATIONS with Geo Sphinx]</ref> [[Solomon W. Golomb]] coined the term ''Rep-tiles'' for self-replicating tilings. ===Applications=== It is a long-term goal of some engineering sciences to achieve a '''clanking replicator''', a material device that can self-replicate. The usual reason is to achieve a low cost per item while retaining the utility of a manufactured good. Many authorities say that in the limit, the cost of self-replicating items should approach the cost-per-weight of wood or other biological substances, because self-replication avoids the costs of [[labour (economics)|labor]], [[capital]] and [[distribution (business)|distribution]] in conventional [[factory|manufactured goods]]. 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 an [[Intel]]'s [[Pentium]] 4 CPU.<ref>http://www.niac.usra.edu/files/studies/final_report/883Toth-Fejel.pdf</ref> 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. A variation of self replication is of practical relevance in [[compiler]] construction, where a similar [[chicken and egg]] problem occurs as in natural self replication. A compiler ([[phenotype]]) can be applied on the compiler's own [[source code]] ([[genotype]]) producing the compiler itself. During compiler development, a modified ([[Mutation|mutated]]) source is used to create the next generation of the compiler. This process differs from natural self-replication in that the process is directed by an engineer, not by the subject itself. ==Mechanical self-replication== {{main|self-replicating machine}} An activity in the field of robots is the self-replication of machines. Since all robots (at least in modern times) have a fair number of the same features, a self-replicating robot (or possibly a hive of robots) would need to do the following: *Obtain construction materials *Manufacture new parts including its smallest parts and thinking apparatus *Provide a consistent power source *Program the new members *error correct any mistakes in the offspring On a [[nano]] scale, [[Assembler (nanotechnology)|assemblers]] might also be designed to self-replicate under their own power. This, in turn, has given rise to the "[[grey goo]]" version of [[Armageddon]], as featured in such science fiction novels as ''[[Bloom (novel)|Bloom]]'', ''[[Prey (novel)|Prey]]'', and ''[[Recursion (novel)|Recursion]]''. The [[Foresight Institute]] has published guidelines for researchers in mechanical self-replication.<ref>[http://foresight.org/guidelines/ Molecular Nanotechnology Guidelines<!-- Bot generated title -->]</ref> The guidelines recommend that researchers use several specific techniques for preventing mechanical replicators from getting out of control, such as using a [[broadcast architecture]]. For a detailed article on mechanical reproduction as it relates to the industrial age see [[mass production]]. ==Fields involving study of self-replication== Most of the research has occurred in a few areas: *[[Biology]] studies natural replication and replicators, and their interaction. These can be an important guide to avoid design difficulties in self-replicating machinery. *[[Meme]]tics studies ideas and how they propagate in human culture. Memes require only small amounts of material, and therefore have theoretical similarities to [[virus]]es and are often described as [[viral]]. *[[Nanotechnology]] or more precisely, [[molecular nanotechnology]] is concerned with making [[nano]] scale [[assembler (nanotechnology)|assemblers]]. Without self-replication, capital and assembly costs of molecular machines become impossibly large. *Space resources: NASA has sponsored a number of design studies to develop self-replicating mechanisms to mine space resources. Most of these designs include computer-controlled machinery that copies itself. *[[Computer security]]: Many computer security problems are caused by self-reproducing computer programs that infect computers — [[computer worm]]s and [[computer virus]]es. * In [[parallel computing]], it takes a long time to manually load a new program on every node of a large [[computer cluster]] or [[distributed computing]] system. Automatically loading new programs using [[mobile agent]]s can save the system administrator a lot of time and give users their results much quicker, as long as they don't get out of control. ==Self-replication in industry== ===Space exploration and manufacturing=== The goal of self-replication in space systems is to exploit large amounts of matter with a low launch mass. For example, an [[autotroph]]ic self-replicating machine could cover a moon or planet with solar cells, and beam the power to the Earth using microwaves. Once in place, the same machinery that built itself could also produce raw materials or manufactured objects, including transportation systems to ship the products. [[Von Neumann Probe|Another model]] of self-replicating machine would copy itself through the galaxy, sending information back. 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]].<ref>http://en.wikisource.org/wiki/Advanced_Automation_for_Space_Missions</ref> 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 [[Aluminium]]. 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 cell]]s 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]] [[molding (process)|mold]]s. 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 [[electricity|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=== [[Nanotechnology|Nanotechnologists]] in particular believe that their work will likely fail to reach a state of maturity until human beings design a self-replicating [[assembler (nanotechnology)|assembler]] of [[nanometer]] dimensions [http://www.MolecularAssembler.com/KSRM/4.11.3.htm]. 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 [http://www.MolecularAssembler.com/KSRM/3.23.4.htm]. 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 [[alternative biochemistry]]. ===Industrial assembly=== [[Image:Advanced Automation for Space Missions figure 5-29.gif|thumb|right|A simple form of machine self-replication]] ==See also== * [[Artificial life]] * [[Astrochicken]] * [[Autopoiesis]] * [[Complex system]] * [[DNA replication]] * [[Life]] * [[Robot]] * [[Reprap]] * [[Space manufacturing]] * [[Universal Constructor]] * [[Virus]] * [[Von Neumann machine]] * [[Self reconfigurable]] * [[Final Anthropic Principle]] ==References== {{reflist}} * von Neumann, J., [[1966]], ''The Theory of Self-reproducing Automata'', A. Burks, ed., Univ. of Illinois Press, Urbana, IL. * [http://www.walenz.org/vonNeumann/index.html Online version of von Neumann's book] * [[s:Advanced Automation for Space Missions|Advanced Automation for Space Missions]], a 1980 NASA study edited by [[Robert Freitas]] * [http://www.MolecularAssembler.com/KSRM.htm Kinematic Self-Replicating Machines] first comprehensive survey of entire field in 2004 by Robert Freitas and [[Ralph Merkle]] * [http://www.niac.usra.edu/files/studies/final_report/pdf/883Toth-Fejel.pdf NASA Institute for Advance Concepts study by General Dynamics]- concluded that complexity of the development was equal to that of a Pentium 4, and promoted a design based on cellular automata. * ''[[Gödel, Escher, Bach]]'' by [[Douglas Hofstadter]] (detailed discussion and many examples) * Kenyon, R., ''Self-replicating tilings'', in: Symbolic Dynamics and Applications (P. Walters, ed.) Contemporary Math. vol. 135 (1992), 239-264. * http://www.cs.bgu.ac.il/~sipper/selfrep/ The Artificial Self-Replication Page [[Category:Artificial life]] [[Category:Biology]] [[Category:Nanotechnology]] [[es:Autorreplicación]] [[de:Autoreplikation]] [[ja:自己複製]] [[tr:Kendi kendini üretim]]