XVIII.2 The nature of the biological evolution is determined by the need to constantly adapt to cumulative and irreversible changes in the environment

As an enormous number of very varied and frequently very intense biotic factors act on a living organism, it can be assumed that most selection pressures acting on a biological species will follow from the action of biotic factors.Thus, the nature of biological evolution is substantially affected by the nature of these selection pressures, i.e. primarily the necessity of adapting to consistent cumulative and irreversible changes in the biotic environment.This obviously has a fundamental impact on the progress of evolutionary processes and on the type of traits that are formed through its action.Directional selectioncan function effectively in the long term only in systems in which acyclic changes in the conditions occur permanently.Under constant conditions, all the existing genetically determined variability in important traits is relatively rapidly exhausted, i.e. advantageous alleles are fixed and disadvantageous ones disappear from the gene pool (see II.7).However, as soon as acyclic changes gradually occur in the environment, the selection coefficients of the individual alleles also gradually change and the genetically determined (and thus selected) variability remains retained for a long time (see VIII.4.4).s

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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
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.