Originally posted by: KIAman
Interesting replies. Strangely, I never thought of viruses as "bugs" in the code of the universe but it seems to fit.
Also, call me stupid, but I had no flippen idea that the human genome contains viruses. I wonder if their genetic code has contributed anything to our humanity... Does this apply to all living things?
Hard to say for sure, but almost certainly all mammals. I haven't looked much at the genome analysis of plants, protists etc. Certainly viral genes have contributed to what we are. We might still be something without them, but imo it's impossible to say what.
From what we've seen so far, I guess viruses do serve a purpose in evolution by weeding out weak genetics.
They don't exist to "weed out" anything. They exist to reproduce. If the host happens to die, so be it. In some cases they might kill the (apparently) strong instead of the weak. Keep in mind that the vast majority of viral infections don't kill the host, it's a rare virus that has a significant mortality rate.
Rhinovirus is an immensely successful virus, and it almost never kills its hosts... just causes a cold.
Ebola has a very high death rate, but it's not easily passed from human to human - one reason being that people die too quickly to pass it on. This is one reason that it's thought that humans are not the natural hosts for Ebola, it's probably something else. Bats seem like a decent guess at the moment.
There's also some speculation that HIV is evolving to a less lethal/debilitating phenotype - if its hosts are healthier and able to live longer, the virus is more likely to spread. Reasonable theory, but I'm not aware of any data that clearly demonstrates it.
But is this truly the case? It seems that if viruses do wipe out a weak genetic variant, then the strong genetic variants propagate but then the virus needs to continue to survive so they evolve to attack the stronger genetic variants and the cycle goes on.
Some of the virus/host game isn't strong vs. weak, it's more like rock paper scissors. Is rock better than scissors? If the virus is paper, then scissors is better. But if the virus is rock then scissors is screwed. Another way of saying it is that the genes that provide resistance to virus A might cause susceptibility to virus B and vice versa. Thus, it's a good thing humans are genetically diverse at some of these crucial genes, it makes it less likely that a single killer virus can wipe us all out.
Now certainly there are some "weak" genetics, e.g. people with genetic immune deficiencies and we do see pathogens removing them from the gene pool pretty efficiently. But these are rare and not really important in the global propagation of the pathogen. A successful virus must be able to infect and spread from normal human hosts. Otherwise it wouldn't be here.
Finally, viruses having their own viruses... I don't know what to say other than... wow?!? I had thought viruses lacked a reproductive mechanism and their sole reason to attack cells to take advantage of their factories.
"viruses having viruses" is sort of misleading.. afaik, viruses don't/can't infect other viruses. It doesn't really even make sense. But they can have parasitic relationships with each other. The example I'm familiar with is Hep D. Hep D is incapable of completing a round of infection in a cell by itself, it requires some Hep B genes to do so. IOW it can only successfully infect a cell that is also infected with Hep B. It parasitizes Hep B genes to complete its own lifecycle. Hep D apparently only encodes 2 genes (!). You really don't want Hep D by the way.