In the meantime, the classification of viruses remains unclear. Tupanviruses seem to be dependent on their hosts for very little, and other viruses, according to one preprint, even encode ribosomal proteins. “The gap between cellular organisms and viruses is starting to close,” Deeg said.

“It’s remarkable that viruses seem to mingle into the translational domain so extensively,” said Matthias Fischer, a virologist at the Max Planck Institute for Medical Research in Germany who was not involved with either study.

If all giant viruses turn out to share translation-related genes that are unique to their group, then it would mean they had a large common ancestor, an ancient virus that diversified over time, and it would lend support to the idea that giant viruses started out big and constitute their own domain of life.

That mingling has sparked contentious debate among scientists about when and how giant viruses evolved. All of viral evolution is murky: Different groups of viruses likely had very different origins. Some may have been degenerate “escapees” from cellular genomes, while others descended directly from the primordial soup. “Still others have recombined and exchanged genes so many times in the course of evolution that we will never know where they originally came from,” Fischer said.