Sir Sebright effect

Selection-determine differentiation of populations or individuals living under various conditions could be the mechanism responsible for the Sir Sebright effect (Flegr 2002). Darwin apparently first described this effect at the level of whole populations (Darwin 1868, Part II, pp. 115 – 117, 143) and Lysenkoists claimed to have observed it at the level of individual plants in their experiments in the 1930’s. Darwin described the experience of domestic animal breeders, according to which it is necessary to occasionally rejuvenate the breeding by crossing animals of the same race that have been bred for a long time under very different conditions. For this purpose, breeders kept one herd of domestic animals in the lowlands and one in the mountains and occasionally performed crossing between the animals in the two herds. This empirically tested procedure, for which a theoretical basis was long sought without success, continues to be used by breeders to the present day in some cases.  The most probable explanation of this phenomenon assumes that certain alleles are selected in a herd that is maintained under the same conditions for a long time, which gradually reduces the genetic variability of the population by elimination of other alleles (Flegr 2002). In two herd kept under different conditions (in lowlands and in mountains), different alleles are selected each time. If the animals from the two herds are occasionally mixed together and crossed, the original genetic variability of the population is renewed, so that some advantageous heterozygote genotypes with high viability begin again to be produced. Renewal of the original genetic variability can also reverse the consequences of gradual micro-evolution, during which the action of natural selection under the particular conditions can lead to a gradual increase in the fitness of members of the population at the expense of their production efficiency.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more