The Role of Positive Feedback in Formation of Macroevolutionary Trends by the Example of Adaptation of Terrestrial Pulmonates (Mollusca, Gastropoda) to Moist Litter

摘要

Morphological adaptations of terrestrial pulmonates (shell reduction, formation of a streamline shell shape, and the development of aperture armature as a conchologieal mechanism of shell management) to locomotion in the lower layers of leaf litter are described. These adaptations are thought to be accompanied by the formation of evolutionary cycles with positive feedback. The cycle includes the following elements: (1) the effect of the environmental factors on the organism; (2) the initiation of theadaptive response; (3) the emergence of evolutionary constrains as side results of the adaptive response, which canalize subsequent changes; and (4) the development of specialization. The elements of chance in the macrocvolutionary processes appear to he due to the selection of adaptive responses. The emergence of a positive feedback system results in the formation of macroevolutionary trends.