Self-replication is any behavior of a dynamical system that yields construction of an identical or similar copy of itself. Biological cells, given suitable environments, reproduce by cell division. During cell division, DNA is replicated and can be transmitted to offspring during reproduction. Biological viruses can replicate, but only by commandeering the reproductive machinery of cells through a process of infection. Harmful prion proteins can replicate by converting normal proteins into rogue forms. Computer viruses reproduce using the hardware and software already present on computers. Self-replication in robotics has been an area of research and a subject of interest in science fiction. Any self-replicating mechanism which does not make a perfect copy (mutation) will experience genetic variation and will create variants of itself. These variants will be subject to natural selection, since some will be better at surviving in their current environment than others and will out-breed them. Overview Theory Early research by John von Neumann established that replicators have several parts: A coded representation of the replicator A mechanism to copy the coded representation A mechanism for effecting construction within the host environment of the replicator Exceptions to this pattern may be possible, although none have yet been achieved. For example, scientists have come close to constructing RNA that can be copied 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. The requirement for an outside copy mechanism has not yet been overcome, and such systems are more accurately characterized as "assisted replication" than "self-replication". Nonetheless, in March 2021, researchers reported evidence suggesting that a preliminary form of transfer RNA could have been a replicator molecule itself in the very early development of life, or abiogenesis. 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 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. Autotrophic 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