quasispeciesn.
/ˈkweɪzʌɪˌspiːʃɪz/, /ˈkwɑːzɪˌspiːʃɪz/, /ˈkweɪzʌɪˌspiːsɪz/, /ˈkwɑːzɪˌspiːsɪz/, U.S. /ˈkwɑziˌspiʃiz/, /ˈkweɪˌzaɪˌspiʃiz/, /ˈkwɑziˌspisiz/, /ˈkweɪˌzaɪˌspisiz/ Biology.
1. A race or type of plant or animal which appears superficially to be a distinct species, or is named by some as though it were such, but is regarded (esp. by later workers) as not warranting such status. Also in extended use. Now rare.
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1839 C. H. Smith Nat. Hist. Dogs (Naturalist's Libr.: Mammalia IX) I. 96 Naturalists..have very generally acquiesced in the doctrine of the varieties (quasi species) of man, as descending, after the great catastrophe of the deluge, from several of the highest ranges of mountains in Asia and Africa.]
1847 H. C. Watson Let. 12 Apr. in C. Darwin Corr. (1988) IV. 31 Assuming Alopecurus pratensis & A. alpinus to be only quasi-species, the Siberian intermediate would be another case in point.
1876 A. Gray Darwiniana vi. 239 He [sc. A. de Candolle] surmised that, notwithstanding the general stability of forms, certain species or quasi-species might have originated through diversification under geographical isolation.
1953 Bull. Torrey Bot. Club 80 227 Numerous geographic races [of blackberry] currently classed by enthusiasts as quasi-species [are] listed under the appropriate major taxa.
1980 W. R. Catton Overshoot iv. ix. 148 The members of a single species discovered ways to behave almost as if they were many different species. Technology facilitated this useful differentiation of one species into many ‘quasi-species’.
2. Originally (in models of evolutionary selection): a group of similar but non-identical DNA or RNA molecules, with a distribution centred on a hypothetically ideal sequence, resulting from a balance between mutation and selection pressure. In later use also: a population of viruses with genomic sequences of this nature.
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1977 M. Eigen & P. Schuster in Naturwissenschaften 64 550/2 The single (molecular) species..is not the true target of selection... It is rather the quasi-species, i.e., an organized combination of species with a defined probability distribution which emerges via selection... The quasi-species is closely correlated to what is called the ‘wild-type’ of a population.
1988 Proc. National Acad. Sci. U.S.A. 85 6814/2 The result is a multitude of nonidentical FMDVs [= foot-and-mouth disease viruses]... Each group is a complex distribution of variants, in agreement with the quasispecies model proposed by Eigen and colleagues to describe nucleic acid clones during early evolution of life.
1995 L. Garrett Coming Plague (new ed.) xi. 378 Within clades were so-called quasispecies, swarms of HIV types commonly found within individual AIDS patients, varying genetically by less than 10 percent.
2002 J. L. Achord Understanding Hepatitis 67 By virtue of natural selection, quasispecies tend to be more resistant to treatment than the parent virus and represent a mechanism by which the virus may escape host defenses and the effects of drugs.
This is a new entry (OED Third Edition, December 2007; most recently modified version published online March 2022).
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