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Wednesday, 8 April 2015

Viruses - origin and other anomalies

During my April 7 blog on viruses, I was quite surprised to notice that there is a lot of debate about the origin of viruses. Astrobiologists Chandra Wickramasinghe and Fred Hoyle believe that some component of the 1918 flu pandemic arrived to earth by meteorite; as the first to be infected were birds. If that were the case then it would be proof of extraterrestrial life as viruses carry DNA.

Viruses are considered by some to be a life form, because they carry genetic material, reproduce, and evolve through natural selection. However, they lack key characteristics (such as cell structure) that are generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life". (Wikipedia)

A Russian botanist, Dmitri Ivanovsky (1864-1920), is considered the first man who described viruses in his 1892 article on a non-bacterial pathogen infecting tobacco plants. In 1898, a Dutch microbiologist and botanist, Martinus Beijerinck (1851-1931), was to first to discover the tobacco mosaic virus and thus evidencing the earlier Russian claim. He is considered one of the founders of virology. (Wikipedia)

Since 1898, about 5,000 viruses have been described in detail, although there are millions of different types. The average virus is about one one-hundredth the size of the average bacterium. Most viruses are too small to be seen directly with an optical microscope. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity.

The word virus is from the Latin vīrus, referring to poison and other harmful liquids. Its existence was "first" mentioned in a compendium called "De proprietatibus rerum" ("On the Properties of Things") by Bartholomeus Anglicus (<1203-1272), dated at 1240, and an early forerunner of the encyclopedia and one of the most popular books in medieval times. The work was organised in 19 books. Book 7 was called "De infirmitatibus" or "On diseases and poisons". Bartholomew carefully notes the sources for the material included, although, at present, it is sometimes impossible to identify or locate some of them. His annotations give a good idea of the wide variety of works available to a medieval scholar. (Wikipedia)

Viruses are found wherever there is life (as they need a host to replicate) and have probably existed since living cells first evolved. The origin of viruses is unclear because they do not form fossils. Currently, there are three main hypotheses that aim to explain the origins of viruses: regressive hypothesis, cellular origin hypothesis and coevolution hypothesis. In the past, there were problems with all of these hypotheses. Viruses are now recognised as ancient and as having origins that pre-date the divergence of life into the three domains. In short, we have NO clue.

In fact, viruses have lived - and thus survived - longer than any other life form on Earth (humans, animals, plants or whatever). One could even argue that all extinct species were killed by viruses. Following that thought pattern, one could even argue that our entire evolution is driven by viruses. In that context, evolution was necessary to survive from relentless virus attacks. Perhaps evolution is first triggered by "updates" to the immune systems of life forms.

In other words: that which does not kill us makes us stronger. (Friedrich Nietzsche)