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Variation of DNA can be found in different mechanisms of genetic change: mutations, recombinations, copying errors, ... In order to find a metasystem transition, we need a mechanism that controls or constrains such changes in a non-random way. Although geneticists are still learning a lot about the underlying molecular processes, there is one mechanism which is clearly not the effect of random noise, sexuality. It can be defined as the constrained variation of DNA sequences by recombination with a second sequence from another organism of the same type.
Sexuality makes it possible to increase genetic variety without the dangers of random mutation: since both sequences have proven their viability, is it not very likely that their recombination would be unviable. Mutations, on the other hand, are most likely deleterious. Higher variety (or "diversity" in biological terminology) of offspring implies a lower probability that all of them would be eliminated by natural selection, and a high probability that at least one of them would be more fit thna the parents. The effectiveness of recombination mechanisms for exploring large fitness spaces has been demonstrated in computer applications by genetic algorithms.
The metasystem that emerges from this metasystem transition is the species, which is defined as the set of all organisms that are capable to recombine their genes in the way mentioned. In sexual organisms, no individual organism really reproduces, since the offspring is always genetically different from the parent. The only system that can really be said to maintain and reproduce is the species as a whole, characterized by a more or less stable "gene pool", i.e. the collection of genes available for recombination.
Reference: Heylighen F. (1995): "(Meta)systems
as Constraints on Variation: a classification and natural history of metasystem
transitions", World Futures: the Journal of General Evolution
45, p. 59-85.