Question

When taken into the larger context of evolution, Professor E believes it is harder and harder to not consider viruses "alive". His arguments that viruses exhibit certain parallels to cellular life might include: (SELECT ALL THAT APPLY--MORE THAN ONE ANSWER POSSIBLE).

1. Viruses increasingly seem to have had, at least early on, a unique evolutionary trajectory as evidenced by their apparently unique set of replicating proteins.

2. Viruses face the same difficulties as cellular life in order to maximize their reproduction.

3. Viral mutations can be said to affect the fitness of the virus, and be either beneficial or deleterious to the virus.

Answer 1

Viruses increasingly seem to have had, at least early on, a unique evolutionary trajectory as evidenced by their apparently unique set of replicating proteins.

Viruses face the same difficulties as cellular life in order to maximize their reproduction.

“The mere fact of the existence of a universal biology unifying viruses and cells now justifies the construction of a Tree of Life that embraces viruses side by side with cells.” says Caetano-Anolles. The interesting thing about these results is that they indicate that viruses must have diversified from ancient cells by a process called reductive evolution, where organisms simplify instead of becoming more complex. Viruses were likely “more cellular in nature and existed in the form of primitive cells,” explains Nasir. The ancient cells that these primordial viruses resided in were those of the last universal common ancestor that preceded diversified life about 2.45 billion years ago.

At some point, the genomes of these ancient viral cells were reduced or eliminated, to the point where they lost their cellular nature and became modern viruses. Nasir says that “viruses restore their ‘cellular’ existence today when they enter and take control of any cell.” When an infected cell spits out new viruses, it is likely very much like those ancient cells making primitive viruses. “Thus,” Nasir concludes, “in the beginning, virus plus cell existed as a unit. Today, they are split but can restore their association upon viral infection of a cell.”