I once wondered, how could a restriction enzyme possibly evolve? It wouldn’t make sense for a cell to carry around an enzyme for cutting it’s own DNA into pieces, should one spontaneously arise. I then realized, it didn’t. Viruses did, which infected cells, and used those enzymes to insert it’s own DNA into the cell. The genes encoding these restriction enzymes in turn mutated, altering their specificity such that they instead targeted viral DNA. The irony being that viruses then ultimately gave prokaryotic cells the means to combat viruses.
In a similar way many genes in eukaryotic cells that are in some sense responsible for our existence, has their origin in ancient viral infections. This is not to say that this is the purpose or use of viruses.
Right. I obviously can see the ways that viruses have contributed to evolutionary innovation in the long-term, both by horizontal gene transfer and by co-evolution. (CRISPR is also based on bacterial anti-viral defenses.) I’m wondering about non-evolutionary benefits of viruses for human health.
I could imagine a possible regulatory effect on the microbiome, with the slight possibility of limiting opportunistic pathogens, but I don’t recall ever seeing any papers supporting this idea. How about you, @mercer?
Interesting ideas. I hadn’t considered the former, but I too was thinking about the latter since the microbiome is itself an ecosystem. It’s not hard to imagine some phages performing key roles in the ecosystem structure, protecting a keystone species or something like that.
I wasn’t thinking of any of this as evidence for or against ID. I was just struck by how confidently Behe makes that claim without any evidence (that viruses play important roles in human health) but rejects a claim for which there is an abundance of circumstantial evidence (that viruses could mediate evolutionary innovation through horizontal gene transfer). I suppose I should be used to that kind of thing by now. But somehow I’m not.
Right. From a design point-of-view, I find the role of occupying-a-niche-so-that-something-worse-doesn’t rather unsatisfying, but since I don’t hold a design point-of-view, no sweat off my back!
Well also keep in mind that the microbiome includes myriad eukaryotes (fungi mostly) that will coexist and coevolve with non-phage viruses. I don’t think there is any evidence whatsoever that these kinds of interactions affect human health, but it wouldn’t be surprising to discover that some did.
We actually still don’t know how viruses originated and while there are at least three competing theories (progressive, regressive, and virus-first), most virologists aren’t solidly in one of the camps because there’s just not enough evidence for one model over another. Most think that viruses are polyphyletic, though, owing to the fact that some branches simply have nothing shared between them. So maybe each model is correct, but for different Realms. (I believe there are four and they do not unify in a higher taxonomic rank.)
