XVIII.1 Changes in the biotic factors in the environment are cumulative and irreversible

While the abiotic factors in the environment are more or less stable on the time scale of biological evolution, or only fluctuate cyclically or randomly in time, changes in the biotic factors in the environment tend to have a cumulative character and are frequently irreversible.The irreversibility of changes in biotic factors is a result primarily of the irreversibility of macro-evolutionary processes, anagenetic and cladogenetic processes in biological evolution.Stochastic processes constitute an important factor in these processes, whether genetic mutations or mass extinction caused by catastrophic events in the environment.Although the environment otherwise changes periodically, for example when there is a periodic alternation of warm and cold periods, species react to these cyclic changes through irreversible evolutionary changes.For example, Dollo’s law expresses the irreversibility of evolutionary processes.According to this law, an organ that disappears during the evolution of a certain species never reappears in the future in its original form, even if the relevant selection pressures that led to its formation in the original species are renewed.It is not necessary to emphasize that, similar to all biological laws, Dollo’s law also has a number of exceptions.

            The biological species that occur at a particular moment constitute a key factor in the evolution of the biosphere.The fact that these species undergo cumulative and irreversible evolution means that changes in the biosphere as a whole also have a cumulative and irreversible character.

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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.