Protistology 2 (1) 6-14 (2001)
The principle of counter-directional morphological evolution and its significance for construction the
megasystem of protists and other eukaryotes
Lev N. Seravin
Biological Research Institute of St. Petersburg State University, St. Petersburg, Russia Summary
Summing up, the following conclusions can be made.
1. Evolution of living systems follows the principle (law) of counter-directional morphological evolution, according to which
both gradation and degradation of organisms can take place.
2. Combination of progressive and regressive changes in the structure of living creatures leads to the appearance of new
taxa of any rank, including very high one (class, phylum, etc.).
3. In different groups of living organisms progressive and regressive morphological changes or their combination can result in
the appearance of very similar but not identical taxa (e.g. sister taxa). The law of irreversibility of evolution should be substituted by a
broader and more accurate law. It can be called the law of non-identity of similar structural transformations in different taxa of living
organisms.
Key words: morphological evolution, progressive and regressive evolution, Dollo's law
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