GENE NETWORKS AND COMPLEXITY OF BIOLOGICAL
ORGANIZATION
N.A. Kolchanov, V.V. Suslov, D.P. Furman
Institute of Cytology and Genetics SB RAS, Novosibirsk, Russia
Emergence of new organisms and their correlation with the evolution of ecosystems is
an important problem. Paleontologic data suggest three global evolutionary trends, namely,
increases in (1) complexity of organisms, (2) number of structural types of ecosystems and
degree of their isolation (however, a complete isolation has never been achieved), and (3)
taxonomic diversity in ecosystems. Dynamics of these trends are phasic—a geologically short
“evolutionary explosion” is followed by a long evolutionary stasis (although molecular
genetic data demonstrate that the evolution does not stop during the stasis). No distinct
correlations between these changes and external (cosmic) factors have been found, forcing
researchers to search for the reason underlying the dynamics of trends in organization of the
living systems per se. The common features of pro- and eukaryotic gene networks (GN)—
block-based hierarchical structure and overlapping of subnetworks (blocks)—suggest certain
common mechanisms of rapid evolution. These mechanisms involve rearrangement of
relations in GN due to mutations of few genes, central regulators. Negative feedback loops
(NFL) may “neutralize” such mutations, thereby slowing the evolution. NFL destruction due
to a change in the selection vector may expose the previously “neutralized” mutations and
lead to the explosive evolution. Abundance of NFL of various natures at all the levels of life
organization (from molecular genetic to ecosystemic) implies a similar principle in evolution
of ecosystems, which complies with ecological data. Genomic sequencing demonstrated the
correlation between complexity of prokaryotes and size of their genomes. However, no such
correlation exists in eukaryotes. Molecular genetics and mathematical modeling discovered
the limitations on increase in prokaryotic genomes, reflecting the features of their
organization (small gene regulatory regions), evolution (horizontal transfer of genes), and
ecology (bacterial mats). The haplodiplophase cycle, removing these limitations, allowed
eukaryotes to complicate their gene regulation through enlarging their regulatory regions,
while the mechanisms of block–module evolution (crossover, splicing, sex, etc.) permitted a
radical increase in the complexity independently of the genome size.