Are viruses our oldest ancestors?

Are viruses our oldest ancestors?

Humans have a skewed view of viruses because we only notice them if they cause disease. In reality, however, viruses are much more than pathogens. HIV and influenza cause frightening health threats, but 10¹⁹ HIV particles worldwide are basically nothing compared to 10³³ total number of viruses on our planet. Viruses are present in every species and every ecological niche, and affect every organism. They even influence the global climate by regulating the population densities of microorganisms—and thereby nutrient availability—in the oceans.

Bacteriophages are the most successful entities on our planet as judged by their abundance, their efficiency in replication and gene transfer and their ability to adapt. Almost all phages have replaced RNA with double-stranded DNA genomes; they are the front-runners in evolution, whereas RNA plant viruses seem to be the laggards—this could be explained with the vastly different replication rates of their hosts. It might also explain why cut-and-paste DNA transposition is active only in plants; in mammalian genomes, it terminated about 35 million years ago and jumping retroelements increased genome size and diversity.

EMBO reports (2012) 13, 1033

Marine viruses major players in the global ecosystem

Viruses are by far the most abundant 'lifeforms' in the oceans and are the reservoir of most of the genetic diversity in the sea. The estimated 10*30 viruses in the ocean, if stretched end to end, would span farther than the nearest 60 galaxies. Every second, approximately 10*23 viral infections occur in the ocean. These infections are a major source of mortality, and cause disease in a range of organisms, from shrimp to whales. As a result, viruses influence the composition of marine communities and are a major force behind biogeochemical cycles. Each infection has the potential to introduce new genetic information into an organism or progeny virus, thereby driving the evolution of both host and viral assemblages. Probing this vast reservoir of genetic and biological diversity continues to yield exciting discoveries.

Nature Reviews Microbiology 5, 801–812 (1 October 2007)

Infectious History

We should think of each host and its parasites as a superorganism with the respective genomes yoked into a chimera of sorts. The power of this sociological development could not be more persuasively illustrated than by the case of mitochondria, the most successful of all microbes. They reside inside every eukaryote cell (from yeast to protozoa to multicellular organisms), in which they provide the machinery of oxidative metabolism. Other bacteria have taken similar routes into plant cells and evolved there into chloroplasts—the primary harvesters of solar energy, which drive the production of oxygen and the fixed carbon that nourishes the rest of the biosphere.

Science 14 April 2000: Vol. 288 no. 5464 pp. 287-293

Joshua Lederberg*