Stabilizing selection prevents evolutionary alteration of characters if they retain their adaptive significance (i.e., the environmental conditions that have caused the corresponding adaptations remain unchanged). However, species usually exist for hundreds of thousands and even millions of years, and the environment does not remain constant in this period. Therefore, stabilizing selection can account for the maintenance of certain characters but not for the long-term existence of species in a phenotypically unchanging state. The latter phenomenon, referred to as evolutionary stasis, is the result of the interaction of intraspecific, inter-population, and biogeocenotic processes. The most important of them is the counterbalance of directional selection vectors, i.e., the scenario in which selection in a certain direction is counteracted by selection in the opposite direction, which prevents the establishment of new characters Balanced polymorphism, i.e., the existence of ecological races and, probably, subspecies with different adaptive strategies, which ensure their adaptation in different subniches of the realized species niche, makes the species more resistant to fluctuations and directed alterations of ecological conditions. Population declineor death of a certain morph or race upon the impairment of its life conditions is compensated by the survival of other morphs (races), which provides for the survival of the species as a whole. The displacement of biome boundaries caused by climate change entails the displacement of species ranges, with the ecological connections characteristic of these species being preserved. This provides for the efficiency of the counterbalance of natural selection vectors and the dynamics of intrapopula-tion and intraspecific structures. The intraspecific mechanisms maintaining the evolutionary stasis are independent of biogeocenotic factors and operate irrespective of whether the biogeocenotic environment remains the same or changes.
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