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Mass Extinctions, Ancient Viruses May Hold Clues to Life's Origins

09 April 2009

Throughout Earth's history, meteorite impacts and volcanic eruptions have repeatedly caused mass extinctions on our planet, often wiping out entire species. But one very old virus that lives at the bottom of the ocean may have survived the extinction events that occurred at the surface. For ages, these ancient crenarchaeal viruses have thrived in extremely hot, acidic environments, where they infiltrate hosts called acidophilic hyperthermophiles ("acid and heat lovers"). The viruses come in extremely diverse morphologies, including spheres, light bulbs, bottles, tulips, polyhedrons with tails, and more.

In a recent study, Matti Jalasvuori and Jaana K.H. Bamford of the University of Jyväskylä in Jyväskylä, Finland, have questioned why crenarchaeal viruses are so diverse among themselves, and yet unlike any other living organisms known today. The scientists developed a model to explain the origins of these differences, based on the idea that the crenarchaeal viruses and their hosts evaded extinction, and so could be one of the most primitive and unchanging life forms that exist today.

With this premise, the model has further implications for how life evolved from its origins to the complex cellular systems we see today. According to the model, extinction events accelerated the evolution of life on earth by eliminating old dominating species and making room for new ones – an idea also supported by previous studies. But Jalasvuori and Bamford take this idea a step further, and suggest that life may have never achieved the complexity necessary for the development of multi-cellular organisms without extinction events that stopped viruses from controlling evolution.

As their model shows, when an extinction event occurs that kills off many of the cells in an environment, the number of viruses also decreases for lack of hosts. Normally, organisms must constantly evolve under pressure from viruses, updating their anti-virus strategies. But under virus-free conditions, organisms can inherit mutations that are likely to be more useful in the long run, rather than simply evolving defensive strategies. In this way, extinction events may speed up the development of new biological functions that otherwise would be unlikely to emerge.

"I find the idea that viruses face extinctions along with their hosts important," Jalasvuori told ( "It is widely believed that viruses, in a sense, control the evolution of their hosts. Some of the novel evolutionary innovations observed today might have emerged for the first time in the genomes of [organisms in a virus-free environment]." 

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