Possibility spaces and evolution.

Regulatory sequences, protein active sites, and gene networks contain evolutionarily conservative modules, which define possibility spaces, which restrict variability and canalize evolution. This provides a new insight into Vavilov's law of homologous series and other cases of parallel evolution. These modules are self-sustained due to duplications and convergent molecular evolution. At the same time, protecting some mutations from the effect of natural selection, the modules facilitate accumulation of mutations in the quasineutral mode and, thereby, promote further evolution, making it unique. [ABSTRACT FROM AUTHOR]