Evolution of the genomic systems of prokaryotes and its momentous consequences.
The earliest self-reproducing cell on Earth, our common ancestor, was probably as small as present-day bacteria. It gave rise to a very large and durable clone whose descendants must have been the only living occupants of the oceans for about one thousand million years. They reached astronomical numbers of separate, disjunct cells, and synthesized many new genes. Their small volume could not accommodate ever larger genomes and useful new genes replaced resident, less successful sequences, thus increasing diversity and the number of strains with highly specialized, distinct, bioenergetic potentialities. Also, selective pressure favored strains able to participate successfully in division of labor and in the sharing of diverse abilities in mixed communities, counterbalancing the limited capacities of individual genomes. Lateral gene transfer mechanisms appeared and were progressively improved, furthering the development of diversity. The prokaryotes' constructive evolution resulted in the formation of a worldwide web of genetic information, and a global bacterial superbiosystem (superorganism). By contrast, eukaryotic evolution of organisms has been typically Darwinian. Diversification of eukaryotic organisms was, however, considerably enriched and accelerated by symbioses with prokaryotes. The more broadly diversified bioenergetic potential of prokaryotes considerably increased the diversity of eukaryotes. Without their participation, our biosphere would have remained much less diverse and less dynamic. Environmental homeostasis has been maintained all along by guided bacterial evolution.