So, in class, we touched a little bit on viruses when we were defining what constitutes life. I think we eventually came to the conclusion that viruses are not alive, but that got me thinking: if viruses aren't alive, where did they even come from?
After a little research, I found that there are three main theories as to how viruses came to be the infectious, flu-inducing, fun little friends we know today: the Virus-First Theory, the Reduction Theory, and the Escape Theory.
The Escape Theory hypothesizes that viruses evolved directly from cells. Supporters of this theory imagine a vesicle enclosing a small part of a cell's genome and "escaping" the cell, forming a membrane-bound body of genetic material. This would account for the similarities we see amongst viruses and their host genomes.
The Reduction Theory finds the birth of viruses in a primordial, parasitic cell that lived its life buried inside another cell, sucking away resources as parasites do. Scientists think this parasitic cell eventually left its host, losing some of its cellular machinery in the process, and thus, became permanently dependent on a host, like viruses we see today. However, one would expect to see strong genomic similarities between viruses and some of the smaller parasitic cells of today, but this is not what we see.
Finally, the Virus-First Theory (which I am rather biased towards) makes WAY more sense! This proposes that before life even evolved, viruses were the reigning leaders of the primordial soup. It's not hard to imagine these somewhat simple, protein-bound containers of genetic material are ancestors of the complex cells that we see today. Some support for this theory includes the fact that viruses are the most physically abundant and genetically group on Earth, which would make sense if they've been evolving for even longer than cells. Also, while many parts of the cellular genome are conserved in viruses, there are many parts of the viral genome that are NOT conserved in cells. Where would viruses have gotten these virus-exclusive parts of their genome if the evolved from cells?? Also also, it would explain why viruses remain universally compatible and can infect across all three domains of life if viruses were the predecessors of all three domains of life.
Many people refute the Virus-First Theory because it violates the fundamental definition of viruses in that they rely on a host to survive. How could viruses have survived if they came before the cells, whose machinery they need to live, you may ask? Well, my friend, who says a viral host has to be a cell? The primordial soup that these viruses would have evolved in would have been ridden with complex molecules, including proteins. It is quite possible that viruses could have used the extra-cellularviral environment as machinery for manufacturing a capsid coat, especially considering that viruses have been co-evolving with cells for a long time; the machinery they use now is probably very different from the machinery they used back then.
Welp, this has been a long, drawn-out rant about why viruses are the king. Comments/discussion/you're-totally-wrong-Shay are all welcome. :)
