Evolution: viruses are key players (original) (raw)

The Origin and Evolution of Viruses as Molecular Organisms

Nature Precedings, 2009

Viruses are the most abundant life forms and the repertoire of viral genes is greater than that of cellular genes. It is also evident that viruses have played a major role in driving cellular evolution, and yet, viruses are not part of mainstream biology, nor are they included in the Tree of Life. A reason for this major paradox in biology is the misleading dogma of viruses as viral particles and their enigmatic evolutionary origin. This article presents an alternative view about the nature of viruses based on their properties during the intracellular stage of their life cycle, when viruses express features comparable to those of many parasitic cellular species. Supporting this view about the nature of viruses is a novel hypothetical evolutionary model for their origin from parasitic cellular species that fused with their host cells. By losing their membrane and cellular structure within the host cell, these new types of parasitic species gained full access to precursors for the syn...

What roles for viruses in origin of life scenarios

Important roles in origin of life (OL) scenarios have been and still are attributed to viruses. Yet the strict dependence of viruses on cells for their multiplication has been widely acknowledged since the first decades of the 20th century. How could viruses play critical roles in the OL if life relies on cellular organization and if viruses are defined as parasites of cells? In other words, how could viruses play a role in the emergence of cellular life if the existence of cells is a prerequisite for the existence of viruses? This paper investigates this issue and describes past and current OL scenarios conferring viruses with important roles, thereby completing the work of historian of science and physician Scott Podolsky who identified three major roles of viruses in past OL scenarios. Some objections raised by present OL scenarios conferring viruses with an important role are discussed. I argue that disagreements concerning the roles of viruses in OL scenarios stem from the different concepts of life and of virus scientists defend. Investigating the roles of viruses in OL scenarios not only helps identifying different ways to define life in the context of OL theorizing. It also offers the opportunity to better understand how viruses could be conceptualized. The relevance of the replication-first versus metabolism-first dichotomy in OL theorizing is briefly discussed.